get_counter, get_ascii, get_varchar added. Used existing methods.
decimal data type. Added method get_decimal. Deserialization into int32 or int64 or double. Checking if the conversion is possible to each type. Consistency tests for this deserialization for each type.
Merge branch 'master' of https://github.com/jacekkasprzak/cpp-driver into dev

Conflicts:
	src/cql/internal/cql_message_result_impl.cpp