Add compiler built-ins (#685)
Add compiler built-ins (#685)

* Add compiler built-ins

Resolves #684

Largely from eyeballing `kotlin_builtins` in the stdlib. The list gets somewhat long though, not sure if we want to maybe run with some sort of higher level structure (i.e. something like `Builtins.STRING` or something)

* Add unsigned types

square/kotlinpoet,square/kotlinpoet