Use glsl-unit for WebGL shaders

[glsl-unit](https://code.google.com/p/glsl-unit/) provides a number of utilities for writing WebGL shaders, including:
 * minification, including synchronized variable renaming between JavaScript and GLSL code
 * unit testing
 * libraries of GLSL functions

This PR adds the use of glsl-unit. Although the code size savings are very modest (704 bytes uncompressed, 134 bytes compressed), I anticipate that, with the complex functionality in the WebGL vector shaders, the code size savings will become more significant and that the library and unit testing functionality will become more useful. It's also nice to be able to edit GLSL code in a separate file with syntax highlighting, rather than editing long strings embedded in JavaScript.

Random notes:
 * since most developers will not be writing GLSL code, I've included the generated JavaScript output; developers do not need to install glsl-unit
 * the version of glsl-unit in npm (0.0.7) is broken, you have to use the latest master
 * the generated JavaScript does not pass the linter in strict mode due to long lines and the mustache templating system's deletion of empty lines, and so these files are excluded from the `lint` target