Would like to contribute to your *heatmap* fork during a few months

Hi! I'll be implementing a heatmap integration during the upcoming months. I'd like to contribute to your fork with new features + docs + more extensive tests and whatnot!

Here's the first 2 commits, basically clean-up, meta-docs, TODOs, Sphinx compatibility and such.

**Note:** This is the first time I'm making a pull request (ever). Though I'm not a total newbie -- have been using Python as my go-to language for 4 years now. Anyhow, please let me know if I'm doing it wrong!