Close #56.

- Use psych instead of syck with Ruby 2.0 series without changing the
  actual method call.
- Fix "syck has been removed" error reported to users by sending the
  error to /dev/null.
Merge branch 'pull-reqs/silence_syck_has_been_removed_error' of git://github.com/CodeGnome/metric_fu into CodeGnome-pull-reqs/silence_syck_has_been_removed_error
Toggle yaml engine to syck if available