Keyboard: Port of TMK XT USB Converter (#3619)

* Converter: add XT USB converter from TMK

* Converter: port TMK code for USB converter to QMK

* Apply requested changes after code review by @drashna

- use "pragma once" instead of include guards
- use LAYOUT instead of KEYMAP
- allow customisation with matrix_init_user() and matrix_scan_user()
- set BOOTLOADER instead of BOOTLOADER_SIZE
- Add XT_ENABLE to OPT_DEFS

* Remove unnecessary lines

tmk_core/protocol/xt.h

@@ -0,0 +1,71 @@
+/*
+Copyright 2018 Jun WAKO <wakojun@gmail.com>
+Copyright 2016 Ethan Apodaca <papodaca@gmail.com>
+
+This software is licensed with a Modified BSD License.
+All of this is supposed to be Free Software, Open Source, DFSG-free,
+GPL-compatible, and OK to use in both free and proprietary applications.
+Additions and corrections to this file are welcome.
+
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright
+  notice, this list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright
+  notice, this list of conditions and the following disclaimer in
+  the documentation and/or other materials provided with the
+  distribution.
+
+* Neither the name of the copyright holders nor the names of
+  contributors may be used to endorse or promote products derived
+  from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef XT_H
+#define XT_H
+
+#define XT_DATA_IN()        do { \
+    XT_DATA_DDR  &= ~(1<<XT_DATA_BIT); \
+    XT_DATA_PORT |=  (1<<XT_DATA_BIT); \
+} while (0)
+
+#define XT_DATA_READ()      (XT_DATA_PIN&(1<<XT_DATA_BIT))
+
+#define XT_DATA_LO()        do { \
+    XT_DATA_PORT &= ~(1<<XT_DATA_BIT); \
+    XT_DATA_DDR  |=  (1<<XT_DATA_BIT); \
+} while (0)
+
+
+#define XT_CLOCK_IN()       do { \
+    XT_CLOCK_DDR  &= ~(1<<XT_CLOCK_BIT); \
+    XT_CLOCK_PORT |=  (1<<XT_CLOCK_BIT); \
+} while (0)
+
+#define XT_CLOCK_READ()     (XT_CLOCK_PIN&(1<<XT_CLOCK_BIT))
+
+#define XT_CLOCK_LO()       do { \
+    XT_CLOCK_PORT &= ~(1<<XT_CLOCK_BIT); \
+    XT_CLOCK_DDR  |=  (1<<XT_CLOCK_BIT); \
+} while (0)
+
+
+void xt_host_init(void);
+uint8_t xt_host_recv(void);
+
+#endif