Render tables without vertical rules and horizontal rules of varying
thickness (with additional space above and below) using the booktabs
package.

This is a rebase of original commit which was on master branch prior to
2.1 release.  In this rebase the \RequirePackage{booktabs} has been
removed from sphinx.sty, as it has to be conditional on latex_booktabs
(or whatever its name will be) configuration option, and will be
repositioned in a subsequent commit.

Render tables with alternating background colors for even and odd rows
(so called "zebra striping").

This is a combination of 28 commits...

- Simplify a bit a conditional in the longtable template

  This also puts the target for a longtable with a label but no caption
  above the toprule for better hyperlinking (testing shows hyperlink
  target can not end up alone at bottom of previous page).

- Refactor and trim doc about LaTeX tables... to make room for more,
  later

- Enlarge allowed syntax for colour assignments via 'sphinxsetup'

- latex_table_style new configuration value and coloured rows

  For the user interface tried to look for inspiration in
  https://docutils.sourceforge.io/docs/user/config.html#table-style
  which mentions booktabs and borderless.  They also mention
  captionbelow which we can implement later, now that architecture
  is here.  They don't mention coloured rows.

- Test on our own document... looks fine!

- Update LaTeX table tests and templates

  Modify longtable templates to put LaTeX macros each on its line

  Table body insertion without removing previous EOL may give output
  which contain some empty lines but longtable defines \par token to be
  same as \empty.

- Work-around an incompatibility of \cline with row colours, improve
  docs

- Reverse priority of classes to allow overruling booktabs by standard
  after parsing source but before letting LaTeX writer act

- Closes sphinx-doc#8220

  Commit
  sphinx-doc@bb859c6
  already improved a bit, this finishes it (as :rst:dir:`rst-class` was
  actually not linking to anywhere).

- Update CHANGES for PR sphinx-doc#10759

- Let booktabs style defaults to *not* using \cmidrule.  They actually
  don't make much sense there, as all \hline's are removed.

- Enhance customizability at LaTeX code level (via code executed prior
  to table rendering, e.g. from a container class environment).

- Patch booktabs \cmidrule, as if it used via \sphinxcline, there is
  a vertical space problem in case of there are two in the same row
  due to booktabs \futurelet not knowing \sphinxcline

- Add \sphinxnorowcolor which allows construct such as this one in
  a tabularcolumns directive:

    >{\columncolor{blue}\sphinxnorowcolor}

  else LaTeX always overrides column colour by row colour

- Add TableMergeColorHeader, TableMergeColorOdd, TableMergeColorEven
  so single-row merged cells can be styled especially

- Extend row colours to all header rows not only the first one
  (all header rows will share same colour settings)

- Auto-adjust to a no '|'-colspec for optimal handling of merged cell

- Add \sphinxcolorblend

- Needed to also detect if a '|' is in tabularcolumns, tests updated

- Fix refactoring in this series which broke table.colsep update

- Add test which would have shown regression regarding table.colsep

- Fix another regression regarding \sphinxcline + booktabs

  Can not add test for that, because it shows only after PDF build.

- Final testing and code comments update

This is a combination of 7 commits.

- LaTeX command \sphinxbuildwarning for important warnings

- Fix some white gaps in merged cells of tables with vlines and
  colorrows

- Work around LaTeX's \cline serious deficiencies for complex grid
  tables

  This commit corrects \cline badly impacting vertical spacing and
  making tables look even more cramped as they usually are in LaTeX
  (although one sees it clearly only with \arrarrulewidth a bit more
  than the LaTeX default of 0.4pt).

  Most importantly this commit solves the problem that \cline's got
  masked by colour panels from the row below.

- Fix regression from a \kern erroneous displacement; and other problems
  with merged cells and colours

- LaTeX code comments and rearrangements of code order

Perhaps this should actually be default behaviour for booktabs +
colorrows at sphinx-doc#10759 ?

Then it would not be an option at all and would not need documentation.

On seeing output in our own document PDF, I find this rather nice
actually.  Perhaps it is indeed better than leaving the white gaps.

Relates sphinx-doc#10759

This avoids at high level of zooming, depending on PDF viewers a line of
non-coloured or anti-aliased pixels at the joining of two rectangles of
same colour due to rounding effects.

Nota Bene: the background colour panels extend a tiny bit beyond left
and right limits of table due to another parameter used for similar
reasons motivated by horizontally merged cells:
    \sphinxcolorpanelextraoverhang
(also defaulting to 0.1pt)

Relates sphinx-doc#10759

This is a combination of 4 commits

- some code comments for future edit if this is to be used upstream

- safer usage of \spx@table@crazyfork in case #1 turns out to be \par

- add \sphinxifthistablewithcolorrowsTF to simplify coding

- \sphinxbooktabsspecialruleoverhang for perfect same-colour-joins

One reason in particular is that the colour is applied only up to the
long table width, but the continuation hints may be larger than this
width (but this width is hidden to not influence the table cells layout).

This way, custom user replacement code for
    \sphinxbooktabs{top,mid,bottom}rule
is relatively painless to inject in preamble or via container class.

Also, it was needed to add some LaTeX code to the longtable template in
order to avoid a colour-related problem with \sphinxbottomrule.

The 'sphinxsetup' key now named booktabscolorgaps defaults to being true
and is left only as a way to provide an easy "turn-off" if the issue
with the longtable colours after the mid rule and above the bottom rule
is blocking to some.  But a priori I envision at 6.0.0 to simply remove
this undocumented option as the said issue is not serious and more to be
considered a fact-of-life.  Besides using booktabs+colorrows is strictly
opt-in at this time.  I considered various LaTeX ways around this
longtable thing (it constructs headers and footers once and for all, one
can not let them depend on some "dynamic" context; there is no easy way
for a body row to know it is first on the page after header, and anyway
would require adding mark-up or considerably complicate the \everycr))
but none of them are even remotely reasonable.

Also, a non-documented booktabsnogaps 'sphinxsetup' key has been added:
it suppresses all the extra spacing booktabs injects around its top,
mid, and bottom rules.  Will solve the booktabs+colorrows+longtable
conundrum from previous paragraph.

This is better not to overload our template.  Besides it makes it easier
for user to use another longtable template.

Remove in passing a note from latex.rst which was of no real use to
Sphinx LaTeX users.