constraints now use a render property
fixed issue with extending null properties
added Common.colorToNumber and Common.log
appease jshint
improved custom engine renderer passing
render will now manage sprite images passed as paths
constraints now support visibility
MouseConstraint is no longer a composite (as it has only one constraint)
added ids to constraints
added pixi.js webgl renderer
added gui option to switch renderer
debug text now respects metrics.extended
refactored and optimised renderer, performance improvements
updated demo
demos are now jshinted
fixed a leak in grid broadphase
reduced dev build file size (chrome inspector was choking...)
updated edge build with all the latest improvements