Updated syntax in drawing demo
Viewport meta for mobile test suites
Use `instances` property for test cleanup
New tests for retina flag
Added `instances` property to global `Sketch` object
Viewport meta for test page
Updated tests to adapt to whether mouse/touch events can be simulated.
Persistant `mouse` object
Clearer labelling of WebGL dependant tests that are expected to fail on certain devices/browsers
Added some examples to the README