Added 2 new sourcemaps features

This adds 2 sourcemaps features that will allow Sentry to work with the source maps generated by browserify:

Loading data URI source maps. The allows you to include your source map as a base64 data uri inside you generated source to avoid having to have a publicly available source map in a seperate file: [mdn.io/data-URIs]()

Parsing inlined source content. The v3 spec for source maps adds the sourcesContent field, which can contain an array of strings which contain the contents of the original source files in the sources field. see line 6 of https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit?pli=1#heading=h.qz3o9nc69um5