CMakeLists.txt

On provides a way to create
- server socket (listening to a given port)
- accept connections
- client socket that can connect to an host:port
these three functionalities are the only ones accessible from pugs'
language

On the other hand, reading and writing are provided by low level
calls. On can exchange values or arrays of values (pointers+size). It
remains unclear if we should allow transfer of higher level objects,
since socket exchanges should be generally used between different
codes?