documentation: update News for 4.14.0 release

[Octachron]

This PR updates the release-info/News file in preparation of the imminent 4.14.0 release.
It is also the right place for bikeshedding my current list of release highlights:

OCaml 4.14.0 (?? March 2022)

• Integrated support for "go to definitions" in Merlin
• Improved error messages in particular for module-level error
• Standard library: new modules In_channel and Out_channel,
  many new functions in Seq module, improved utf encoding support.
• Runtime optimisation: GC prefetching
• Deprecated functions and modules in preparation for OCaml 5
• Tail modulo cons transformation
• Work-in-progress: refactorisation of the type checker
• Many other quality of life improvements
• Many bug fixes

[gasche]

Tail modulo cons transformation

I suggest to add (experimental) at the end to manage expectations.

[gasche]

Potential new things to mention

• Add UTF codec and validations support to the Stdlib #10710: Add UTF tools, codecs and validations to the Uchar, Bytes and
  String modules.
  (Daniel Bünzli, review by Florian Angeletti, Nicolás Ojeda Bär, Alain
  Frisch and Gabriel Scherer)

(this is arguably mentioned in the list but in a very unclear way I think?)

• Allow explicit binders for type variables #10437: Allow explicit binders for type variables.
  (Stephen Dolan, review by Leo White)

(This Changes entry could be completed with actual code examples, one for val and one for existentials in GADT constructors.)

• Support more arguments to tail calls by passing them through the domain state #10595: Tail calls with up to 64 arguments are guaranteed to be compiled
  as tail calls.

Potential things to remove

If I had to make space, I would drop "refactorisation of the type checker" (this is not visible to most users) and "many other quality of life improvements" / "many other bug fixes" (this is not informative), and then TMC (this is for advanced users only).

Suggested changes

Runtime optimisation: GC prefetching

You should give some numbers of potential gains to expect (for programs that spend a lot of time in the major GC).

Deprecated functions and modules in preparation for OCaml 5

Maybe mention that in particular Stream and Genlex are deprecated?

[dbuenzli]

I agree with @gasche that this is a confusing way to put it. We had encoding support for quite some time :–)
I suggest , string and bytes UTF decoding and validation support.

[Octachron]

I would propose

- Standard library: new modules In_channel and Out_channel,
  many new functions in Seq module, UTF decoding and validation support
  for strings and bytes.

to reduce the size of the prefixed part of the nominal group.

[Octachron]

An argument for mentioning the refactoring of the typechecker is that both the changes at for classes and type expressions might end up visible through the prism of unexpected bugs. But the highlight are probably not the right place for that pessimism.

The number of highlights is quite reasonable for now. I think it make sense to add the explicit binder syntax and the new guarantee for the tailcall optimisation:

• Integrated support for "go to definitions" in Merlin.
• Standard library: new modules In_channel and Out_channel,
  many new functions in Seq module, UTF decoding and validation support
  for strings and bytes.
• Runtime optimisation: GC prefetching. Benchmarks show a speedup of around 20%
  in GC-heavy programs.
• Improved error messages in particular for module-level error.
• Deprecated functions and modules in preparation for OCaml 5.
  In particular, the Stream and Genlex modules are now deprecated.
• Type variables can be explicitly introduced in value and variant constructor
  declarations. For instance,

    val fold: ('acc -> 'elt -> 'acc) -> 'acc -> 'elt list -> 'acc
    type showable = Show: a * ('a -> string) -> showable

can now be written as

    val fold: 'acc 'elt. ('acc -> 'elt -> 'acc) -> 'acc -> 'elt list -> 'acc
    type showable = Show: 'a. 'a * ('a -> string) -> showable

• Tail-call with up to 64 arguments are now guaranteed to be optimized
  for all architectures.
• Experimental tail modulo cons (TMC) transformation
  (with some expected future breaking changes on the horizon).

[wikku]

Suggested change

	type showable = Show: a * ('a -> string) -> showable
	type showable = Show: 'a * ('a -> string) -> showable

[Octachron]

Fixed, thanks!