Fix monospaced fonts in docs

The monospaced font used in `tt` and `code` elements does not match.  This is only made obvious if the monospaced font is customized in the browser to something other than the ones specified for `code` in our css.

![screenshot](https://f.cloud.github.com/assets/38294/1360166/b8f8a8f2-37f0-11e3-9cf1-bb44ac13d9fa.png)

This PR is in two commits.  The first should be uncontroversial (it just makes the fonts match).  The second changes to using the open source `Inconsolata` font, downloaded from the Google font service.  This will make the docs look the same on all platforms.  Using "Monaco" as the default was not a great choice because it comes from Apple and is only licensed for use on a Mac.  (This is also the font we use in the LaTeX version of the docs, FWIW).