Haxe 4 operator keyword

[eliasku]

Seems like the latest Haxe 4 dev build reserve operator identifier as a new keyword

[nadako]

I've merged #114 for time being, but we'll have to think about what to do with this problem in future. Surely, Haxe 4.1 will get some way to support it, but before that, an abstract that forwards field access to reflection might work.