The LPC class now has properties for getting and setting echo, baudrate,
and stopbits.  Low-level access is now private to avoid letting users
break the public properties.

Also, a new write_ram method implements the W command.  If no number of
bytes is specified, the length of the data is used.

Now we have code to connect to the serial port, put the LPC into ISP
mode, unlock the flash, and update echo and serial port settings.  The
code's way nicer than lpc21isp so far, which is all I really wanted I
guess.