Adds Goodreads and extract TOC plugin, git ignore rules and fixes latex module

I have added a plugin that can be used to display user's Goodreads activity. It's properly documented.

Besides, Goodreads activity plugin, extract TOC is also part of this pull request. Extract TOC extracts table of content from `article.content` and places it in `article.toc`. It is required so that user can put TOC of his article in `<nav>` tag or display it separately from article's content. 

Project didn't have any ignore rules defined. I have added git ignore rules for Python, Vim, Emacs, Windows, Linux and OSX. I think it cover majority of the userbase so this will be useful for other users too.

Lastly, I added `__init__.py` to Latex and Goodreads plugin. Without it, it is hard to figure out how to import plugins into the project. Now all user has to do is to append `pelicanext.latex.latex` to his PLUGINS array.