[Keymap] 🗺️ Adds massdrop/alt/favorable-mutation keymap (#6893)

Features:

* Tap space for space, hold for cmd
* Tap caps lock for esc, hold for ctrl
* Dedicated key for entering default mode of yabai window manager
* Who needs arrow keys, anyways???
* Method for clearing all stuck-down mods

keyboards/massdrop/alt/keymaps/favorable-mutation/config.h

@@ -0,0 +1,28 @@
+/*
+Copyright 2019 Griffin Rademacher <contact@griffin-rademacher.info>
+
+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 Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+// toggle one-shot layer keys after this many presses
+#define ONESHOT_TAP_TOGGLE 3
+
+// set time held before Mod-Tap key sends mod code
+#define TAPPING_TERM 1000
+
+// permissive hold: if holding down a Mod-Tap key while pressing another, it
+// acts as a mod, even within the tapping term
+#define PERMISSIVE_HOLD