Allow access to clues_metadata during jobs perform method

* Added Runtime mixin to provide access to jobs that need it
* Store clues_metadata in a threadlocal dupe
* Merge back data from dupe into original on perform_finish
  or failed
* Updated readme with usage
* cleaned up some specs
* ensure travis builds work on ruby v1.9.3 - v2.1.2
Move towards system data being stored in attrs prefixed with '_'

* System data will be stored in '_' prefixed attrs
* System data will also be stored in non-prefixed attrs to
  preserve backwards compatability
* Future release will remove the data in the non-prefixed attrs
  allowing people to migrate to v1.2, upgrade their dashboards,
  then migrate to v2.0 to have a seamless upgrade path.
Merge pull request #10 from lwoodson/access_clues_metadata_within_job

Allow access to clues_metadata during jobs perform method