(maint) Use MatchData object over ruby global vars

The implementation for native file headers for the ParsedFile providers
made use of the Perl style global variables like $`, $', and $&. These
are difficult to understand at first glance and equivalent behavior is
provided by MatchData objects. This commit removes the global variables
with a MatchData object for clarity.
Merge pull request #1489 from adrienthebo/maint/master/parsedfile-human-readable-match-variables

(maint) Use MatchData object over ruby global vars