Configuration Additions

I added a few options to the configuration so that this theme can be customized without needing to make an extension. All of these options can be completely ignored and the default behavior will remain.

* homepage - When set this replaces instances of "master_doc" in places like the logo, project link and table of contents pages.

* tospage - This replaces the link on the "Table Of Contents" header with a custom page.

* projectlink - This replaces the url in the link off of "project_nav_name". Unlike homepage and tospage, this takes an actual URL instead of a sphinx page in order to allow linking offsite (for cases when your documentation site is not the same as your project's main site).

* navlinks - Takes a list of links (name and url) to add to the navigation menu.

```python
"navlinks": {
  "Blog": "http://blog.myproject.url”,
  "OtherExample": "http://example.myproject.url”,
},
```
* highlight_color - Overrides the default highlighting color (blue) with a user defined setting.

* bodylink_color - Allows the user to further override the color settings by allowing the links inside the content area to be different than those in the navigation menu.