More small changes to the docs.
1. Better landing page.
2. Minor tweaks to the side bar.
3. Reference to more example code.
4. Local MathJax references.
Change-Id: I39b9436dc2803732a875bbbee7f15802c4934031
A live version of the doc can be found at
http://homes.cs.washington.edu/~sagarwal/ceres-solver/
As it stands, the documentation has better hyperlinking
and coverage than the latex documentation now.
Change-Id: I7ede3aa83b9b9ef25104caf331e5727b4f5beae5
Sameer Agarwal