Bumped version to 0.8
Improve ValidationError

* JSON represenation is always a dict now
* "extras" is merged into dict
* "message" is now called "reason"

ValidationError raised from the List validator now exposes
"index" in its JSON representation.
Add "default" kw arg to BaseValidator
Add Dict validator. Improve ValidationError JSON.
Moved schema package into validators and schema mobules
Make test module file names lowercase with underscores
Add "reason_code" to ValidationError
Update CHANGES.rst and small doc string fixes.
Update version in docs/config.py