Supersedence checker based on Microsoft Update Catalog

[DominicBreuker]

Adds a flag --muc-lookup which will lookup all missing patches in the Microsoft Update Catalog to identify superseeding KBs. It then filters the CVEs by checking if any of the superseeding KBs is installed.

This is more of a suggestion that a final product based on what I read in the wiki. Let me know if this does not make sense.

A few notes:

• Did not write any tests but tested manually with Python2 and Python3 for compatibility
• lookups need MechanicalSoup for scraping. Loading it lazily only if --muc-lookup is passed to not force people not interested in the feature to install any dependencies. If you pass the flag and don't have it installed you get an error message telling you to install it.
• this flag will perform online lookups and the update catalog seems slow (at least for me). It may take a lot of time for long lists of vulnerabilities.
• I've added a gitignore with all the default Python entries just because there was none yet.

[bitsadmin]

Wow, great addition Dominic! :-) I am currently a bit busy, but I will test & merge this very nice feature ASAP!

[DominicBreuker]

thx :) ping me if there are bugs and I will look into it!