Fix circle specs (using wrong subject)

Get rid of "global" subject, and explicitly create the "oval" object in
each describe block. We were creating a 'circle' object, but running
specs against an 'oval' object that was inherited from a parent context.
Add stroke and fill specs for creating ovals
Fix spec descriptions to read better
Add specs for creating ovals with hex fill/stroke
Merge pull request #3 from wasnotrice/oval_style

Add specs for creating ovals with hex strings