Added script to generate graph about gerrit

Generates graph using gerrit statistics.
Measures # of remaning review entries over specified time.
Argument parsing using python-gflags
Added readme
Update README.md
Added is:open to stats

Also measures review which status is 'open'.

Flag name for ssl-cert verification updated.
Handle is:open properly

Change sets listed in is:open now measures range from created to `now'.
Fill bars in graph with color using review count