Added dependencies for libYAML
Implemented a YAML configuration parser, fixed DoormanError and renamed it to DoormanException

YAML is great for config files. It is very readable and easy to parse.

A basic configuration will look like this:

/home/user/config.py:
 twitter_password: asdfasdf
 github_password: fdsafdsa

 # some comment
/etc/myconfiguration.conf:
 my_secret: cupcakes
Updated README.rst to cover configuration using YAML