Futhark: Automatic C imports in Nim using libclang

[PMunch]

Futhark understands all macros, as in it processes them until it has valid C 
code. It doesn't support getting values from a macro or call a function-style 
macro yet though. This is simply because C macros are inherently typeless since 
they are just a text replacement. I have a plan for how to wrap them, but it's 
not implemented yet unfortunately.