Add Socket word set.

[SirWumpus]

Following #27 it should much easier to implement a Socket I/O word set, ie. socket, connect, accept, etc. Sockets typically use read, write, close, etc. which can be shared with the File Access words based on POSIX I/O.

• Do we create a 1-to-1 mapping of POSIX I/O words?
• Do we borrow from other Forth implementations such as GForh, VFX so that ready made packages from theForthNet can just drop-in.