Correct the construction of Consumer Control Key objects

There were a few minor problems in the way Consumer `Key` objects were
constructed (using `CONSUMER_KEY()`). First, no masking of the high
bits was being done, so it was possible to create a "Consumer" key
with the `RESERVED` bit set (e.g. `Key_Transparent`), or the
`SWITCH_TO_KEYMAP` bit (in fact, any `Key` value with both the
`SYNTHETIC` and `IS_CONSUMER` bits set was possible).

This change fixes these potential problems by setting the six bits
taht could conflict to zero. When we need to have special behavior
based on those bits, this can change.

src/kaleidoscope/key_defs.h

@@ -1,5 +1,5 @@
 /* Kaleidoscope - Firmware for computer input devices
- * Copyright (C) 2013-2018  Keyboard.io, Inc.
+ * Copyright (C) 2013-2020  Keyboard.io, Inc.
  *
  * This program is free software: you can redistribute it and/or modify it under
  * the terms of the GNU General Public License as published by the Free Software
@@ -225,19 +225,22 @@ typedef kaleidoscope::Key Key_;
 #define SWITCH_TO_KEYMAP           B00000100
 #define IS_CONSUMER                B00001000
 
-/* HID types we need to encode in the key flags for system and consumer control hid controls
-   Each key can only have one, so we don't need to use a bit vector.
-   We need to keep the top two bits clear for defining the keys as synthetic
-   We need to keep the bottom two bits clear for defining the keys as sysctl / consumerctl
-*/
-
+// HID Usage Types: Because these constants, like the ones above, are
+// used in the flags byte of the Key class, they can't overlap any of
+// the above bits. Nor can we use `SYNTHETIC` and `RESERVED` to encode
+// the HID usage type of a keycode, which leaves us with only two
+// bits. Since we don't currently do anything different based on HID
+// usage type, these are currently all set to zeroes.
+#define HID_TYPE_CA    B00000000
 #define HID_TYPE_CL    B00000000
-#define HID_TYPE_LC    B00000100
-#define HID_TYPE_NARY  B00001000
-#define HID_TYPE_OOC   B00001100
-#define HID_TYPE_OSC   B00010000
-#define HID_TYPE_RTC   B00010100
-#define HID_TYPE_SEL   B00011000
+#define HID_TYPE_LC    B00000000
+#define HID_TYPE_MC    B00000000
+#define HID_TYPE_NARY  B00000000
+#define HID_TYPE_OOC   B00000000
+#define HID_TYPE_OSC   B00000000
+#define HID_TYPE_RTC   B00000000
+#define HID_TYPE_SEL   B00000000
+#define HID_TYPE_SV    B00000000
 // Mask defining the allowed usage type flag bits:
 #define HID_TYPE_MASK  B00110000