Added pthread to CMake requirements.
pthrad.h included in globals.h
Added web_client_t and thread_pool_t control structures.

Thread pool would hold a queue of available threads that should service
incoming socket requests. Sockets are blocking therefore we need a
separate thread for each request. 
Needless to say this is not intended to be a larger http server impl. We
wouldn't expect a lot of requests!
Fixed pthread build errors.
Now using a thread per client/new socket request.

This is just a temp solution until the thread pool is implemented.