Add tests and improve code style

[bmesuere]

This branch adds tests to the gem:

• test functionality
• add rubocop style checks
• add travis tests for multiple ruby versions
• add coveralls

This branch introduces these changes:

• 100% test coverage 🎉
• some major refactoring and improved code style
• remove command aliases
• remove --xml download options
• fixes help output for the uniprot, peptfilter and prot2pept commands

Original pull request by @bmesuere on Wed May 20 2015 at 22:54.
Merged by @bmesuere on Fri Jun 12 2015 at 15:42.