Strip all nonalphanumeric chars from package names

Some packages have apostrophes ("astronomer's") and potentially other non-slug-friendly characters.
Bash completion

Bash completion script for tab completing main module commands and package names for `#install` and `#uninstall` commands.
Add `#_listallpackages` pseudo-private method to get package slugs.
Merge pull request #420 from alampros/bash-completion

Bash completion