add ability to read from USB serial

watch-library/shared/watch/watch.h

@@ -76,4 +76,12 @@
   */
 bool watch_is_buzzer_or_led_enabled(void);
 
+/** @brief Reads up to len bytes from the USB serial.
+  * @param file ignored, you can pass in 0
+  * @param ptr pointer to a buffer of at least len bytes
+  * @param len the number of bytes you wish to read, max 256.
+  * @return The number of bytes read, or zero if no bytes were read.
+  */
+int read(int file, char *ptr, int len);
+
 #endif /* WATCH_H_ */

watch-library/shared/watch/watch_private.h

@@ -44,7 +44,8 @@ void _watch_enable_usb(void);
 // this function ends up getting called by printf to log stuff to the USB console.
 int _write(int file, char *ptr, int len);
 
-// this method could be overridden to read stuff from the USB console? but no need rn.
-int _read(void);
+// i thought this would be called by gets but it doesn't? anyway it does get called by read()
+// so that's our mechanism for reading data from the USB serial console.
+int _read(int file, char *ptr, int len);
 
 #endif