User manual pdf generation. Menu options for user guide and feedback

This will add:
- a help menu with options
    - `Circuitscape User Guide` : opens a browser window pointing to 4.0 user guide at github
    - `Discuss / Provide Feedbacks` : opens a browser window to the support page at http://www.circuitscape.org/Support which has the google groups widget embedded
- a `doc` target to the makefile that generates a pdf version of the user guide from the markdown file. The pdf can be generated with `make doc` command. I have also checked in the pdf to github, as we may want to point to it from elsewhere.
- auto generates the `.rst` format README file required for registering python package.

The document format conversions need the `pandoc` utility which can be installed from http://johnmacfarlane.net/pandoc/installing.html.