Add package alias with new name

[msullivan]

Add a gel alias that does import * from edgedb.

Note that this will not provide any submodules.
Doing from gel import errors won't work.

But we also never documented anything internal, and it will all keep
working with an edgedb import, so nothing will break.

If we feel strongly about providing all the internal modules under the
gel name also, we have options, but as far as I can tell they are
all annoying in some way:

• Generate a parallel tree of modules under gel that all do import *
  from an appropriate edgedb module. This is kind of ugly and also
  we need to regenerate when anything changes.
• Something involving hooking the python import system. I think this
  would work but also I think involves modifying global python interpreter
  state when gel is imported, which is dodgy.

I'd probably go with option 1 if we care, but not caring seems fine?

[1st1]

I think we should just rename and tell to people to start using "gel" if they want new stuff.