Uninstall elixirs; remove aliases.

[greymouser]

• Added list of aliases per elixir version to kiex list output
• Add support for removing aliases
• Add support for uninstalling elixir versions (and associated aliases)
• Solves issue #39

[greymouser]

Happy to factor in any feedback. (I haven't heard anything in 14 days -- is this project still active?) Thanks!

[taylor]

Thanks @greymouser.

I'd like to get tests in place at some point so it "feels" safer to pull in updates :)

[greymouser]

Nice! No, thank you, @taylor !

[taylor]

@greymouser reverted because of Bash 3.2 support needed for OS X. See https://github.com/taylor/kiex/issues/63