Merge pull request #9 from reillysiemens/master

Scaffold new Attaché structure. Create installer.
Fix potentially incorrect sourcing of profile

Sorry @reillysiemens!
Add a basic completions files for bash/fish/zsh

Totally one hundred percent copied from rbenv's completions
Also, they don't actually work yet since they depend on two non-existent
subcommands of attache 'completions' and 'commands'
Robustify the unimplemented message

Also, put it to stderr, not stdout