attempt to implement "match_all_files" parameter

This is probably a naive implementation, but it should work.
Make match_all_values work with or without argument
match_all_files: 'true' should be 'True'
Merge: Attempt to implement "match_all_files" parameter

Merge pull request 1
https://github.com/valhallasw/gerrit-reviewer-bot/pull/1