Changes to Exceptions

*   Changed from explicitly declaring __init__ for exceptions but then only using the super().__init__ to just passing.
*   Moved the second Exception declaration so that they would be proximate.
*   Added both Exceptions to the namespaces of requests_toolbelt and requests_toolbelt.multipart
*   Added a test for BodyParts to ensure instances that are attempted to be created with content not containing CRLF/CRLF throw exceptions.