Add method to purge lights without failures

Also well as supporting `delete` method.
Re #23; test more Rubies on Travis CI
Merge pull request #26 from orgsync/gh-23

Officially support Ruby >= 1.9.3, JRuby, and Rubinius
Merge branch 'master' into purge-stale

Conflicts:
	lib/stoplight/data_store/memory.rb
	lib/stoplight/data_store/redis.rb
Fix #19; pass Redis instance to data store
Forward 'delete' and 'purge' from Stoplight
Update changelog
Merge pull request #24 from orgsync/purge-stale

Add mechanism for flushing old lights
Merge pull request #28 from orgsync/gh-19

Pass Redis instance to data store
Merge branch 'master' into gh-21

Conflicts:
	CHANGELOG.md
	README.md