First cut at porting to asm.js

Doesn't at all work yet...
Bugfixes; Working asm.js port!
Use a larger random buffer

We were starved for entropy; the interations went much faster, but they didn't
contribute much toward smoothing the image. Next step is to try a small inline RNG.
Inlined pseudo-random number generator for trace()
Command line option for a debug build
Fix stop condition in lineLoop()

This error was introduced when I was rewriting this for asm.js
Fix for line endpoints
Merge branch 'master' into asmjs
Fake Web Workers implementation for debugging
More conservative clamping; fixes histogram overflow on Chrome
Minimal polyfill for imul

To speed up non-asmjs browsers a little.
Remove obsolete comment
Clearer precedence
Maybe we shouldn't recommend Safari...

Even on the master branch, it's noticeably clunkier than either Chrome or Firefox.
Deferred initialization, small speedups for Webkit
Concurrent support for asm.js and original renderers
Simple feature test for asm.js
Shhhh