Replacing native types by functional names?

[DerKarlos]

We already started to use functional name-types (TileCoord, GeoPos, ...) to make our code more readable, even as a new contributor may be puzzled and has to look and learn the types.

What do you think about this?:

• Replace most/all native vec by functional names
• TODO

[oli-obk]

I think it's gonna be case-by-case, but anything we return from a function should probably have a newtype, yea.