Write SVG contributions data to DOM to parse songs

GitHub’s `/contributions` endpoint switched from JSON to SVG at some
point, breaking data parsing. Instead of parsing the SVG as a string,
write the SVG the DOM to let the user’s browser render it as DOM
elements and use jQuery to traverse the data.

A user’s SVG has an ID of “{user}-data”.

Fixes #27.
Describe function better and use appropriate var name

* A `<div>` wrapping an `<svg>` is passed in, not the `<svg>` itself.
Merge pull request #28 from ssorallen/master

Write SVG contributions data to DOM to parse songs