Rewrite of the tutorial.

1. Quicker starting point.
2. Better discussion of derivatives.
3. Better hyperlinking to code and class documentation.
4. New robust estimation example.
5. Better naming of example code.
6. Removed dependency on gflags in all the core examples covered
   in the tutorial.

Change-Id: Ibf3c7fe946fa2b4d22f8916a9366df267d34ca26