FEATURES:
- Added interfaces extending the attr.Type interface to include attribute and element types. (#44)
- Added state, config, and plan types, and support for getting values from them. (#46)
- Added support for Object types. (#38)
- Added support for bools, numbers, and strings. (#29)
- Added support for defining schemas and attributes. (#27)
- Added support for lists. (#36)
- Added support for maps. (#37)
- Added support for provider, resource, and data source types. (#32)
- Added the ability to serve providers. (#45)