Added ability to retrieve more information on challenge validation failure

[adamzero1]

docs: added docs for accessing validation error messages

refactor: refactored Client class to let challenge object construct itself Meaning the Client object doesn't need to know about all potential fields for the challenge object.

feat: validation error message access Added new variables to the challenge object Added a new Error object This way if a challenge fails to validate, information about why the validation failed can be obtained.