add script to clean up gists

The script cleans up gists from closed/merged PR's.
replaced sse3 option in amd by mavx option
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
added a check for the http return code + download progress report

    * Check the http return code before starting a download, urllib.retrieve does not do this by default
    * show a download report ' X kb downloaded of XXX total kb (XX% complete) xxx kbps'
addressed remarks
check to see if a valid response code was returned, could also be None when offline
fixed typo in xHost option
switched from mavx to xHost
Merge pull request #960 from pescobar/improve_intel_optarch

Improve intel compiler arch optimization when compiling in amd cpus
clean up README
move build statuses to the bottom of the README
fix related repos links
fix homepage URL
cosmetic changes
fix (long) description in setup.py, more cosmetics
fix description
drop title in README