fixes JSDoc formatting in gl-matrix
fixes JSDoc formatting in vec3
Adds an externs.js

These were kind of a pain to generate, so I thought you might want to provide them.  I kept a single copyright preamble in place, and put this in the root directory, let me know if you want me to change either of those.
Oops, wrong branch :(
Merge pull request #132 from nickgeorge/master

Fixes small JSDoc formatting errors in src/vec3 (and correspondingly dist/)