Add pdf version of the documentation

To create the pdf:
```
    cd $CLAW/doc/doc
    make latex
    cd _build/latex
    make
    # then type q when it starts throwing errors that need to be fixed
    pdflatex ClawpackDocs30Nov2014
```

The last step seems needed to make the TOC properly.

Problems:
- Lots of math errors are thrown.
- Various things should probably be omitted, e.g. gallery?