This adds support for the "framer" device, which is a USB-connected
device built around a Raspberry Pico that connects to a synchronous
line, either RS-232 or DEC "integral modem" coax connection. It
implements the framing portion of DDCMP: clock recovery for the
integral modem case, byte sync, and DDCMP frame handling including
CRC. The actual DDCMP protocol state machine, with its handling of
sequencing, timeout and retransmit, etc. is left to the host
software. All the design files for the framer may be found at
https://github.com/pkoning2/ddcmp .
This commit adds code to drive the framer from the TMXR library,
allowing it to be used either from simulated DMC-11 or simulated
DUP-11 devices. Both have been tested, using RSTS/E, RSX-11/M+, and
TOPS-20.
Fixed the one-digit limit on eth<n> device names, the limit is now 2.
