(maint) restrict redcarpet gem to <= 2.3.0

Per the tag annotation from the redcarpet 3.0.0 release, 2.3.0 is the last
version compatible with ruby 1.8.7.

https://github.com/vmg/redcarpet/releases/tag/v3.0.0
Merge pull request #582 from jhoblitt/redcarpet_gem

(maint) restrict redcarpet gem to <= 2.3.0
Merge branch 'stable' into facter-2
(refactor) Remove double negation from resolution confine check
(maint) clean up Facter::Application#run

Move requires to top level, simplify how facts are sorted
(FACT-159) Extract facter command line formatting

This extracts facter's command line formatting to a separate file and
calls out plaintext formatting as a specific case. This allows us a
clean way of removing the plaintext behavior as we move towards
structured facts.