Add an option to send 'a' repeatedly

Change-Id: I81239d802035ecfb760c483b8b0d83c66a643f5d
diff --git a/y2019/jevois/structures.h b/y2019/jevois/structures.h
index b6db24e..676b46c 100644
--- a/y2019/jevois/structures.h
+++ b/y2019/jevois/structures.h
@@ -141,6 +141,9 @@
   kCameraPassthrough,
   // Go to being a useful USB device.
   kUsb,
+  // Send As, which triggers the bootstrap script to drop directly into USB
+  // mode.
+  kAs,
 };
 
 // This is all the information sent from the Teensy to each camera.