Sourcemap paths

![tumblr_mde5kxekvf1rhfw98o1_400](https://cloud.githubusercontent.com/assets/925735/3421995/8532955a-ff0f-11e3-81de-857f802bddf5.gif)

Fixes #17 and #49 and all those other #$&*&^%$ sourcemap issues. Sourcemaps point to the original files on disk. No extra settigs necessary.

A little addition to gulp-intermediate made this easy.
If there are `/`s in the sourcemap paths, serializing to JSON escapes them. The original files aren't escaped. Running it through `new Buffer` removes / uses the escapes.

I'm not sure it matters, but I'd rather output a file in the exact format we get in.