Per-client memory usage reporting feature.
Some additional comments won't hurt.
Fixed building on GCC 4.6.
Some beatifulization.
Merge branch 'memory-usage-reports'
Changelog update.
Minor cleanup.
Merge branch 'master' of https://github.com/andrusha97/cocaine-core into andrusha97-master

Conflicts:
	include/cocaine/api/gateway.hpp
	include/cocaine/detail/gateways/adhoc.hpp
	include/cocaine/detail/locator.hpp
	include/cocaine/messages.hpp
	src/gateways/adhoc.cpp
	src/locator.cpp
Additional stuff for the Routing Groups patch.
Fixed building on GCC 4.4.
Minor improvements.

* 'services_t' has been renamed to 'router_t', because difference between 'services_t' and 'services_list_t' was not clear.
* Some logging messages have been added.
* Router and services list are used under different mutexes, so some operations no longer block each other.