rs: code friendly keymap for preonic, iris and my preonic clone (#4303)

I worked on those keymap to simplify the use of 60% keyboards for
coders. Instead of trying to mimic planck, this keymap remove
raise/lower layer complexity and keep some important sign keys for coder
in the upper right side pretty much the same way as they are on a full
keyboard.

A karabiner configuration is also provided to mimic most of the keymap
features on the macbook internal keyboard for when you are forced to use
it.

layouts/community/ortho_5x12/rs/config.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#ifdef AUDIO_ENABLE
+//#define STARTUP_SONG SONG(PREONIC_SOUND)
+#define STARTUP_SONG SONG(NO_SOUND)
+
+#define DEFAULT_LAYER_SONGS                                                    \
+  { SONG(QWERTY_SOUND), SONG(COLEMAK_SOUND), SONG(DVORAK_SOUND) }
+#endif
+
+#define MUSIC_MASK (keycode != KC_NO)
+
+/*
+ * MIDI options
+ */
+
+/* Prevent use of disabled MIDI features in the keymap */
+//#define MIDI_ENABLE_STRICT 1
+
+/* enable basic MIDI features:
+   - MIDI notes can be sent when in Music mode is on
+*/
+
+#define MIDI_BASIC
+
+/* enable advanced MIDI features:
+   - MIDI notes can be added to the keymap
+   - Octave shift and transpose
+   - Virtual sustain, portamento, and modulation wheel
+   - etc.
+*/
+//#define MIDI_ADVANCED
+
+/* override number of MIDI tone keycodes (each octave adds 12 keycodes and allocates 12 bytes) */
+//#define MIDI_TONE_KEYCODE_OCTAVES 2