Merge from master
Add support for PImage filters. The filters are structured in such a way that they should be usable outside of just PImage (for anything rendering a canvas).

Filters added include threshold, gray, invert, posterize and opaque.
Add docs for PImage.filter()
hold
hold2
returning actual frame rate with getFrameRate() now, and setting default to 60, closes #117
fixing preloadfunc closes #115
adding core unit tests
adding TDD style tests to Core
changed random() unit test to TDD style
removing extraneous test
adding jsdoc comments to random()
fixing test
adding globals for test
implementing random2D(), random3D(), fromAngle() for PVector
unit tests for new PVector methods
new p5.js build
Merge pull request #128 from shiffman/master

Implemented PVector methods
fixing TDD random tests
beginning to add calculation unit tests