Add helix keyboard (#2308)

* Fork from Let's Split

* Organizing files

* Delete some keymaps

* I2C and serial enabled at the same time

* Change readme

* add #define HELIX_ROWS for multiple rows

* Delete avrdude flashing script

* Delete makefiles

* Subproject elimination

* Fix lufa path

* Remove PLAY_NOTE_ARRAY usages to get rid of warning.

Fix conflicting function name

* Mousekey change default to off

* Fix to oled display adjust

* make rev2

change pin assign
change keymap

* use master_buffer

* Timing adjustment

* Organizing files

* Change Keymap

* Change Keymap

Add EISU and KANA
Correct 4rows

* NKRO default to disable

* EXTRAKEY_ENABLE default to disable

* add rgb reset key

* rgb custom function enable

*  Extend font

* add RGBLED_POWER

default folder to helix/rev2
RGB_ENABLE to no

* renamed directory

* Disable RGBLIGHT_CUSTOM_DRIVER

* Disable LOCKING_SUPPORT_ENABLE

* Update bootloader setting

* Change readme

* Fixed argument error

keyboards/helix/readme.md

@@ -0,0 +1,16 @@
+Helix
+===
+
+![Helix](https://i.imgur.com/XBAmynN.jpg)
+
+A compact split ortholinear keyboard.
+
+Keyboard Maintainer: [Makoto Kurauchi](https://github.com/MakotoKurauchi/) [@pluis9](https://twitter.com/pluis9)  
+Hardware Supported: Helix PCB Alpha, Beta, Pro Micro  
+Hardware Availability: [PCB & Case Data](https://github.com/MakotoKurauchi/helix), [Yushakobo Shop](https://yushakobo.jp/shop/)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make helix:default
+
+See [build environment setup](https://docs.qmk.fm/build_environment_setup.html) then the [make instructions](https://docs.qmk.fm/make_instructions.html) for more information.