Make exception behavior more like Java SDK

This ticket makes the .NET sdk return/throw similarly named exceptions for various failure states:

1. DocumentAlreadyExistsException - an attempt to insert a doc that exists
2. DocumentDoesNotExistException - an attempt to replace a doc that does not exist
3. TemporaryLockFailureException - an attempt to retrieve a locked doc
4. CasMismatchException - a doc was modified resulting in a CAS failure

Previously, the IOperationResult.Exception field was null on these cases, however the Status field indicated the failure.