This commit improves the support for documenting the fields found
in request and response payloads. The improvements include:
- Using the term "payload" rather than "state" as the latter is
somewhat HAL-specific
- Code simplification, including the removal of the Path abstraction
- Automatically determining the type of a field based on the payload
that's being tested
- Updating the samples to use the new API
In addition to these improvements, support for documenting field
constraints has been removed as more thought is required. The
FieldDescriptor abstraction is used to describe both request and
response fields, however it's not clear that contraints apply to both
and they certainly don't apply in the same way. For the time being at
least, users who want to document a field's constraints can do so as
part of its description.
Closes gh-24