Preliminary additions for UART discovery support
Working version of UART discovery (8N1 only). Modified Set_Target_Voltage to allow you to turn off target voltage once it's been set. PropUART.spin removed (no need for it, since JDCogSerial already handles the low-level serial routines and the rest of the UART discovery is handled in JTAGulator.spin)
Completed UART discovery (8N1, unused code for parity bit checking). Updated CHANGES.
Added date for Black Hat USA 2013 release