Retain type and field comments in output

[Simn]

See https://github.com/HaxeFoundation/haxe-evolution/pull/65

This requires some busywork in the generators, but other than that shouldn't be controversial.

We need a -D flag to allow configuring this behavior.

[RealyUniqueName]

Php generator already does that by default.

[RealyUniqueName]

I think the targets, which don't care about compiled project size, should do it by default too.