docs: Add and format descriptions of the public API's class, methods, and parameters. (EDU-2484) (#344)
docs: Add and format descriptions of the public API's class, methods, and parameters. (EDU-2484) (#344)

* initial api doc edits

* docs: Add and format descriptions of the public API's class, methods, and parameters. Provide missing descriptions and make the wording consistent with readme.io.

* stylistic edits per Jennifer Black

optimizely/objective-c-sdk,optimizely/objective-c-sdk,optimizely/objective-c-sdk,optimizely/objective-c-sdk