v0.10.1 - Fix `font-size: 0` typing problems and more

Important fix: remove font-size: 0 on textarea (#585), fixing typing
in Chrome Canary (#540) as well as the Enter key not triggering the
enter handler in Webkit and Blink (#566). transform: scale(0) is
used instead and expected to be much more robust.

(Note: if you're coming from v0.9.x, there've been major API changes,
see the v0.9.x → v0.10.0 Migration Guide.)

new features:

• (#544, #552, #558, #581) new symbols \nparallel, \measuredangle,
  \odot, \parallelogram (nonstandard), \nless, \ngtr, \square
• (#544) new commands \overleftarrow, \overrightarrow

bugfixes:

• (#585) fix typing in Chrome Canary, Enter key in Webkit+Blink
• (#582) fix \degree symbol to round-trip (rather than exporting
  ^\circ which doesn't parse as one symbol)
• (#578) fix .text() to output \cdot as *
• (#529, #571, #574) fix .text() of fractions, spaces, variables followed
  by exponents
• (#577) fix \triangle symbol to match LaTeX better
• (#568) hotfix #435 order-dependence breaking clean build on Linux
• (#560) fix florin spacing still too close
• (#546) fix parsing or pasting × (Unicode times symbol)
• (#519/#487) fix auto-horizontal-scroll/pan on API calls
• (#528) fix #429 can't move cursor out of TextBlock
• (#526) fix exponentiation to export ^ not **
• (#525) fix Tab while there's a selection

build system fixes:

• (#532) add console output to show URL of local test pages