Use a less cryptic string format for token.Locations.

Fixes #44.
Remove unused stringStringer type.
Use package pretty, which is prettier than pp.

Also, remove ast.Print and ast.Dot. They aren't needed, since you can just use pretty.Print and pretty.Dot.
Also also, don't use Eq outside of test code

Fixes #43.
Merge pull request #45 from velour/pretty

A few printing fixes.