fixed filter caching and implemented 'isCached' property
now disabling vertex attrib arrays after filter has been rendered (closes #28)

I'm not entirely sure why, but here it's necessary. Otherwise, after using the DisplacementMapFilter once, Sparrow's performance degrades by almost 20 percent!
added 'touchGroup' property to display object containers, and using it in SPButton
margin fix
added "randomFloat"
enhanced quality of displacement map filter on iPad 1 (showed artefacts before)
added 'perpendicular' and 'truncateLength:' methods, normalize is now safe
added factory methods
SP_RELEASE_AND_COPY fix
added uniform scale property
added SP_PHYSICS_CLASS define

if SP_PHYSICS_CLASS is defined before importing Sparrow headers you can
access the property without having to cast to the specific class…
Merge pull request #22 from Gamua/master

Gamua additions
updated copyright dates
GLKView convenience property
removed drawable width/height properties
comment clarity
cleanup
fix, missed a previous commit
fixed some analyzer warnings
Merge pull request #31 from racarone/master

Minor Additions and Cleanup