Match install script closer to thoughtbot's
Rearrange settings between zlogin and zshrc

* Moved settings between the startup files to the best of my understanding of
their differences described here: http://zsh.sourceforge.net/Intro/intro_3.html
* Moved `diff_routes` to its own script located in `bin` directory
* Added more descriptive comments for each setting
Add aginore and gitignore from thoughtbot