improvements to help system

- can now execute 'ebs-deploy -h' or 'ebs-deploy --h' and not get an exception
- can also execute 'ebs-deploy help' and get a help message
removing spurious blank line
refactoring - inlining usage_and_exit method
adding forgotten file help_command.py
Merge pull request #9 from adamfeuer/help-improvements

Help system improvements