Smoother serial

[BillThePlatypus]

Improves performance with serial connections:

• Adds parameters ~wait_for_serial and ~serial_check_period. If ~wait_for_serial is set to true, and the serial port is not available when the node comes up, it will wait ~serial_check_period seconds and then try again, until the node is killed or connects.
• When the serial connection is lost, displays an error message so stating, and closes gracefully, instead of a thread error.
• I'm considering adding the ability to automatically reconnect on a lost connection.

[bsutherland333]

This is something that we've actually talked about improving, funny that work on it already exists. We should definitely finish this up.