Port documentation to be included in this repo

[basicdays]

I can port the documentation from the PyYaml website to just be included in the repo. Outside contributions might be easier to accept in this format perhaps.

Specifically the documentation I'm referencing is from http://pyyaml.org/wiki/PyYAMLDocumentation.

First pass I can do is a straight up port, folks can probably go in and edit things afterwords perhaps. Are there any preferences to the documentation syntax? I've usually just stuck to MarkDown, but I know a lot of Pythonistas tend to use reStructuredText.