expand_path should be called on prefix
Don't expand target
Save the results for popular for no-args functions
Remove unused method
Change option from --nogui to --gui

the default option for --gui is false.

Th new with-gui command becomes
bin/stemcell build ubuntu --gui

instead of
bin/stemcell build ubuntu --nogui false
Fix typo
Merge pull request #11 from anfernee/rhel

Code cleanup