add /commits page, with simple highlighting

This is theoretically the start of some richer, web-based ways of interacting with your local git repository.

Example screen:

![](http://f.cl.ly/items/1Q2r3E3Z3b3j280L0w2U/Screen%20Shot%202014-09-20%20at%203.19.06%20AM.png)

open questions:
* do I need to declare the new py deps, `json` and `pygit2` (which depends on `libgit2`) somewhere?
    * `pip install cffi libgit2 pygit2 json` should do work.
I've never used either, but I've heard from multiple sources that SASS is preferable. If it's not too much work, I'd definitely prefer to learn SASS rather than less.