add script to clean up gists

The script cleans up gists from closed/merged PR's.
clean_gists.py: added options
clean_gists: implement all options

Everything should work now
clean_gists: delete closed pr gists by default
clean_gists: fix bug when description is empty
Use logger from simple_options
Merge pull request #958 from wpoely86/cleanscript

add script to clean up gists