getting key_ codes instead

- changes made to some constants and macros
- changes made to _curses_screen struct
- identified and removed prototypes for yet more unsupportable functions

- wgetch now includes non, part and full blocking read support

we are constructing the IP header ourselves.

Formatting fix-ups (80 column limit is mandatory!)

- some minor preventatives

- no longer depends on slk

- some more minor functionality implemented

- corrected minor algo errors in primitives
- added doxygen @file header

- wdeleteln function implemented

- some optimisation done

transition away from uIP.

Prepared ipv4.c for transition away from uIP.

Kill off the static single net device and move to proper dynamic
registration (which we need with the new device model).

Break the (flawed) assumption that all network-layer protocols can use
ARP; such network-layer protocols (i.e. IPv4) must now register as an ARP
protocol using ARP_NET_PROTOCOL() and provide a single method for checking
the existence of a local network-layer address.

period before updating to the new driver API (which can cope with
having TX packets in progress).

(This actually matters once you try using TCP, because you *will*
receive full-sized frames.)

Shrink to 4kB for now.  We might want to see if it can be made
genuinely indicative of the RX ring size in the new TCP
implementation.

Update rtl8139 driver to instantiate an SPI interface with a three-wire
device attached.