Serial port access from Lua could use additional functions

[zandr]

I just implemented a simple Lua script to turn sensor data from a PLX Devices fluid temp sensor into virtual channels.
The existing serial API seems very line-oriented, and doesn't do well with packet formats that are terminated with things other than newlines. Being able to pass in an extra parameter to readSer() that specified a different termination character would be very useful.
Simliarly, I have to read the serial buffer frequently, even if I'm not using the data, because there's no way to flush the serial buffer. If I could flush the buffer, and read until I get an 0x40, then I could poll the data much less frequently. There isn't much reason to poll trans temperature at 10Hz. :)