Add NIU Mini from KBDFans (#1847)

* Add NIU Mini keymap from Planck keymap

* Remove old keymap files

* Fix README, removed Planck references

* Add default layout, move Planck layout to separate folder

* Update README

keyboards/niu_mini/keymaps/planck/config.h

@@ -0,0 +1,32 @@
+#ifndef CONFIG_USER_H
+#define CONFIG_USER_H
+
+#include "../../config.h"
+
+#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
+
+#endif