parsed DHCP responses.

1. Updated UDP send data code\
2. Corrected internet checksum\
3. Moved udp_buffer() and udp_buflen() to udp.c from udp.h

structure, and populating it with options.  This should allow us to
use the same basic options list for both DHCPDISCOVER and DHCPREQUEST,
plus making it much easier to set the non-constant parameters
(e.g. requested IP address) in request packets.

to search through all registered option blocks.

Move some static inlines that are likely to be used frequently into
dhcpopts.c as normal functions, to save space.

by SSL servers. Framework.c allows me to test the library against a given
https server.

derived is a 16-bit big-endian field, but htype is only 8 bits wide.

is a DHCP option" data structures.

We need this code in order to be able to return a DHCP packet to a PXE NBP
which reflects options from our multiple sources (e.g. NVS and DHCP
server).  This is expensive, but necessary.  Having paid this cost, we may
as well try to use the same code to generate our DHCP request packets,
since the process is similar.

DHCP options block from the contents.

encapsulated option; this will be needed for modifications to the options
block.

- value of n passed to wgetnstr should now be equivalent to output from strlen (i.e. length excluding NUL-terminating character)

- reimplemented cleaner wgetnstr
- fixed wdelch for use with _wcursback

- added mucurses_test.c build targets

multiple option sources (e.g. multiple DHCP replies, non-volatile
storage etc.)

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