Merge pull request #23 from nferraz/master

Simplified code
Add --github|gh argument to pull public  contributions data out of github
( as suggested by dgryski here https://github.com/k4rthik/git-cal/issues/15 )
Breaking up code into smaller units
process_current_repo()
git_command()

Thanks to https://github.com/nferraz
(tried merging https://github.com/nferraz/git-cal/commit/f2cf620c3b328bf3abb037e0136e2dc6925861d1
but too many conflicting changes due to my prev commit :) )
Update README.md
Removed some globals
Fixed conflicts