New APIs and documentation

* The `extend` method replaces the old __setitem__ logic
* Move to sphinx for docs
Another test for
Document metadata
Fixed representation of config objects, allow get_value() of non-leaf configs
Documentation
Configs initialized with None to hold None as a value
Fix path assignment
Documentation, remove no-longer-necessary utils shortcuts
v2.0.0.dev0
v2.0.0.dev1
Add default type for coercion
Version bump