Add support for aliases

[mnewt]

When an alias is created in the bash environment, create the corresponding function in the fish environment

This is something bass added a while back

If you're interested, I may be able to get around to creating a pull request

Cheers!

[mnewt]

Yeah, I couldn't help myself. Please check out #13 and provide feedback. Be aware that it builds on #12. Sorry about that, but they both touch fenv.main