Refactored netbuffer into netpeer

Rolling netbuffer into netpeer (and renaming to netcom) made the API
much cleaner; there was no reason anything needed to know about netcom
or netchan, all that's ever needed is the peer number and what kind of
packet (reliable/unreliable) to send.  This makes the code much simpler
from a semantics point of view: less to keep in mind.

At long last, TOC reading now works properly; now we're very close to
where we were with the old netcode design.

Upgraded from CMP v1 to v2; needed better integer reading API

Fixed bugs stemming from a misunderstanding of M_BufferGetData; I
thought I wrote it so M_BufferGetData returned the whole internal
buffer, but it returned the internal buffer from the current position of
the cursor, so that was causing all sorts of dumb problems.  Refactored
that into M_BufferGetDataAtCursor, created M_BufferGetData to do what I
thought it always did, and pushed those changes through m_pbuf as well.

Fixed some off-by-one errors in m_buf discovered during the development
of CMP

Refactored n_peer to follow the normal function naming convention
(N_PeerGet instead of N_GetPeer, for example)

Rebuilt tags