Impl custom alias names
Oof...this implementation feels very fragile and hacky, and I don't think the extra lines of code are worth the feature of being able to specify an alias name.

Going to pass on this for now. The 3.0 stuff I'm working on can do this as a matter of course, so it'll land then.
 +1 on it for the rewrite.  including the alias equality?

implements https://github.com/coleifer/peewee/issues/972
