small LaTeX related changes to conf.py
changed image file to jpg
changed image references in rst files from gif/png to jpg
added link to gps chapter
added link to "getting nx under Windows" post
Adjustments for LaTeX PDF output

* Split TOC out and add separate overview file
* Add title logo for pdf
* Fix image issues for PDF
Merge branch 'wip'
Small fixes

image names in getnx.rst, stray block quote in gps.rst