Rename has_key? -> key? (BC compatible)

Ruby has moved away from has_key?, so mixlib should as well.
Merge pull request #21 from opscode/sethvargo/key

Rename has_key? -> key? (BC compatible)
Force RSpec 2.x
Fix typos
Merge pull request #22 from mriddle/master

Fix README typos
Revert "Fix README typos"
Merge pull request #23 from mriddle/revert-22-master

Revert "Fix README typos"
Fix strict mode errors to actually print symbol