Add xd75/billypython keymap (#4381)

* Add xd75/billypython keymap

* Expand rules.mk

(cherry picked from commit 806fee94ae3a21b6ca7a34624101349b57d41b75)

* Expand billypython's rules.mk

* Remove unused stuff in whitefox/billypython

keyboards/xd75/keymaps/billypython/config.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#define FORCE_NKRO
+
+#define MAGIC_KEY_LAYER0_ALT1  BSLS
+#define MAGIC_KEY_BOOTLOADER   ESC
+
+#define MOUSEKEY_DELAY              50
+#define MOUSEKEY_INTERVAL           15
+#define MOUSEKEY_MAX_SPEED          4
+#define MOUSEKEY_TIME_TO_MAX        50
+#define MOUSEKEY_WHEEL_MAX_SPEED    1
+#define MOUSEKEY_WHEEL_TIME_TO_MAX  50
+
+#define PERMISSIVE_HOLD
+#define TAPPING_TERM    200
+#define TAPPING_TOGGLE  2