Fix typo in CMakeLists
Added tcp server/client

This first version implements a simple echo server.
Using C++11 threads to control the server service
Revert "Using C++11 threads to control the server service"

This reverts commit 15671a607e39d9e5c875ec79f043651323be12e2.

Using std::threads actually introduces more issues wrt using
boost::threads. In fact it happens that compiling code using std::thread
on linux with GCC requires passing the flag `-pthreads`. So instead of
manually managing platform differences it's better to use Boost as a
bridge to the actual platform at the price of adding one more
dependency (i.e. linking against boost::threads).
Using plain char[] instead of std::array

Clang on linux fails to compile.
Fix segfault on mac

It seems that when not keeping a ref to the thread starting the
io_service may case a segfault when calling ~thread. In order to prevent
this the thread is joined when stopping the server.
Added directories preprocessed header
Using cout for all log messages (waiting for a good log library)
Added COMPILE_FLAGS option to macro add_unit_test
Added EasyLogging++ and usage test
Added logging system
Added protocol and serialization
Using protocol in tcp server/client
Setting the _ELPP_THREAD_SAFE macro
Test protocol with three request type (offline, realtime, upload)

This is still work in progress.
Fix linker error
Moved elpp_test to server module
Using boost::thread instead of std::thread
Merge branch 'develop' into feature/server
Added BaseRequest and three subclasses for Offline/Realtime/Upload