Add alias functionality. Think I've done #4 now.
Amend the packager file to work better with aliases.

I rearranged a loop so that it adds the .js suffix after it checks the
aliases, so that one can specify aliases just like require.js.
Fix some typos and bugs.
Fix two other unused variable errors.
Merge pull request #7 from maxbucknell/4-paths

4 paths. Close #4