Merge #327

Merge #327

327: Beginnings of type inference r=flodiebold a=flodiebold

I was a bit bored, so I thought I'd try to start implementing the type system and see how far I come :wink:  This is obviously still extremely WIP, only very basic stuff working, but I thought I'd post this now to get some feedback as to whether this approach makes sense at all.

There's no user-visible effect yet, but the type inference has tests similar to the ones for the parser. My next step will probably be to implement struct types, after which this could probably be used to complete fields.

I realize this may all get thrown away when/if the compiler query system gets usable, but I feel like there are lots of IDE features that could be implemented with somewhat working type inference in the meantime :smile:

Co-authored-by: Florian Diebold <flodiebold@gmail.com>