Add perl-stable and stable to available perls to install
Add missing completion for install 'blead'
Fallback to filenames on no completions
Add completion for --switch
Use prefix_match instead of our homespun solution
Don't complete libs for uninstall
Offer 'shorthand' completions for installable perls

ex. 5.8.8 instead of perl-5.8.8
Update changelog
Update README
v0.09

     - Tell perlbrew's completion to fall back to filenames if no completions are generated
       (for install)
     - Add missing completion for install ('blead')
     - Offer 'stable' and 'perl-stable' as completions for perl install
     - Add completion for new '--switch' option