Warn in docs that cJSON objects must be freed.
Double the size of all byte buffers to alleviate overflow.

In the precense of a message with many signals (could be up to 64 in a
single message), we are likely to overflow the buffer since it isn't
flushed until we're done parsing and translating all signals in the
message. This may work around #132 for this rare case.
Restore serial port detection by reverting an overzealous regex.