Dev

Contains all the changes in #2 plus `gh-book*`:

- Changed the Github client library to `github-client`
- Added support for loading images through the `github-client` API (support private repositories)
- Parses the entire XHTML files (`<html><head>...</html>`) instead of just assuming the contents of the `.html`file are the children in the `<body>`. (jQuery does not parse full HTML files properly; it strips the `<html>` `<head>` and `<body>` tags out)