DC aware policy feature parity with other drivers

- Refactored DC aware policy
- Added extra unit tests for DC aware
Missed in-place add when host is present
Code review refactor for DC aware local CL setting
Document default dc-aware behavior

and fix small typo
Minor typo from review update.
Merge branch 'CPP-180' into rc1

Conflicts:
	include/cassandra.h
	src/cluster.cpp
	src/config.hpp