FocusSerial: Add Focus.read(char &c)

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

plugins/Kaleidoscope-FocusSerial/src/kaleidoscope/plugin/FocusSerial.h

@@ -94,6 +94,9 @@ class FocusSerial : public kaleidoscope::Plugin {
     color.g = Runtime.serialPort().parseInt();
     color.b = Runtime.serialPort().parseInt();
   }
+  void read(char &c) {
+    c = static_cast<char>(Runtime.serialPort().read());
+  }
   void read(uint8_t &u8) {
     u8 = Runtime.serialPort().parseInt();
   }