Adds filter option to setup module

Adds facts filtering using fnmatch, via the 'filter' option.

Usage:
ansible -m setup -a 'filter=ansible_*_mb'
Adds example for filter option in setup module

Added an example on how to filter keys returned by the module.
Added more examples for the filter option in setup

Added examples covering all available globs
Added a use case of filtering only facts returned by facter
Fixes unused var and avoid reassigning keys

Changed code so key doesn't get reassigned in loop
Made use of filtr variable
Moved key filtering

Key filtering moved before returning results
Optimizes using fnmatch only if needed

Skips fnmatch'ing if there is only a '*' in filter.
Merge branch 'setup_filter_argument' of git://github.com/leucos/ansible into devel
Docs tweak to setup module.