py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for. A
port will also provide mphalport.h with further HAL declarations.
This patch overhauls the network driver interface. A generic NIC must
provide a set of C-level functions to implement low-level socket control
(eg socket, bind, connect, send, recv). Doing this, the network and
usocket modules can then use such a NIC to implement proper socket
control at the Python level.
This patch also updates the CC3K and WIZNET5K drivers to conform to the
new interface, and fixes some bugs in the drivers. They now work
reasonably well.
