Add options for github URL and print-only.

* Use argparse for real cli parsing.
* Add github option to print compare URL and open in browser.
* Add print-only option to only print log or github URL.
* Modify setup.py to support develop mode.
fixup! Add options for github URL and print-only.
Merge branch 'add-github-and-print-only'

Conflicts:
	README.md