Add from_inet for initializing Address
Change to use Address in IOWorker backend

Changing from Host to Address in backend, where extended Host attibutes
should not be needed.
Further conversion of Host-->Address in low-level code

Connection updated
Avoid pool ready callbacks on reconnect.

Prevents the Session::pending_pool_count_ invariant from going negative, when
it should really only be used to count down initial connection attempts.
Control connection cluster node discovery.
don't leak ResultIterator in control connection
Improved error handling

Updates from code review:
- Handle ErrorResponse, unexpected opcode
- Note on queries about dependent indexing
- Minor formatting
Merge pull request #59 from datastax/CPP-145