Makefile.lib: Add support for building C++ sources
libpubnub-cpp: C++ bindings for libpubnub #4940687846331
examples-cpp/sync-demo: Add a simple pubnub-sync C++ demo of the basic API calls
libpubnub-cpp: Change first argument of PubNub_*_cb from PubNub* to PubNub&

It can never be NULL so the code should be cleaner with using PubNub& consistently everywhere in the API.
pubnub_cpp_subscribe_cb(): The channels[] array shall be freed by the callback code
libpubnub-cpp/pubnub.hpp: #include STL prerequisities
example-libevent-demo.c: Clarify a confusing sentence in a comment
examples-cpp/libevent-demo: Add a pubnub-libevent C++ demo showcasing/testing C++ callbacks
libpubnub-cpp/pubnub.hpp: Mention enum pubnub_res, referring pubnub.h

After this change, studying pubnub.hpp should be 'self-contained', not
requiring any prior knowledge of the C API.
README.md: Describe also the C++ bindings
TODO: C++ wrapper built
Merge branch 'CL-4940687846331'