simple reformat (saves 449 minified bytes)

hi,

great, concise lib you got here! thought i'd suggest a slight reformatting of the code to shave quite a few bytes off the minified version. since github's diff cannot ignore whitespace changes, here's what was done:

1. Define the entire `Matrix.prototype` in a single assignment rather than repeating `Matrix.prototype.*` for every method.
2. Indent all methods.
3. Re-minify using Closure Compiler.

This saves 449 bytes off the minified version and improves readability (however slightly).

Looking through your repos, I'm finding a lot of other interesting stuff that's similar to some of my projects. You might like to glance at:

https://github.com/leeoniya/RgbQuant.js
https://github.com/leeoniya/pXY.js
https://github.com/leeoniya/GIFter.js (this one's going through a re-write to deliver on the readme)

thanks for your work!
Leon