[js] support js require
[js] added js.Lib.require (see #2949)
[cs] Add -net-lib support for Compiler.add_native_lib
[cs] minor
[cs/unity] Unity does not support Compiled flag
[js] Add "require" to pseudo-keywords list so a local var with the same name doesn't override the global "require" function.
[python] Builtin.open returns FileIO (with write methods and stuff)
[python] explicitly hint NativeIterable.iterator to avoid type inference problems (see #2979)
[python] fix tuple creation
do not make nonsense monomorphs when calling abstract methods from within the abstract (closes #2979)
[python] clean up NativeIterable/NativeIterator stuff (nonsense type params, static @:to, inlines)
Remove unused var
Merge pull request #2949 from nadako/js_require

[js] support js require
[cpp] Split vector creation from setting the size
[python] do not generate `= None` for optional KwArgs/VarArgs arguments (closes #2980)
also disallow additional arguments after KwArgs/VarArgs
treat "." and ".." as special cases in haxe.io.Path (closes #2956)
CHANGES.txt update [skip ci]
[python] slight improvements/cleanup to python.Boot, allow inlining of Std.string, ArrayImpl use arrayJoin of Boot
mention js changes in CHANGES.txt
fix indenting