Change program usage to be more verbose.

The usage output was changed to include a description of what the
program does, along with some examples for running it.  This matches
how most of the standard command line tools behave (for instance,
`cat`).

This fixes issue 19.
https://github.com/fujimura/hi/issues/19
Add a --help flag to the command line.

This prevents the error `hi: unrecognized option '--help'`.

This is for issue https://github.com/fujimura/hi/issues/18.
Merge pull request #20 from cdepillabout/issue-19-usage-more-verbose

Change program usage to be more verbose.
Merge pull request #21 from cdepillabout/issue-18-add-help-flag

Issue 18 add help flag
Update submodule and specs
Use defined defalt repo in usage