Change BL to use 127 as annouce character to avoid printing

The lower, non-visible ascii characters were showing up in the Arduino terminal window as squares. This fixes that.

Author: Nathan Seidle

tools/artemis/artemis_uart_loader.py

@@ -15,7 +15,7 @@
 from sys import exit
 
 # Bootloader command constants
-BL_COMMAND_ANNOUNCE = 5
+BL_COMMAND_ANNOUNCE = 127
 BL_COMMAND_AOK = 6
 BL_COMMAND_BAD_CRC = 7
 BL_COMMAND_NEXT_FRAME = 8