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

keyboards/converter/xt_usb/config.h

@@ -0,0 +1,78 @@
+/*
+Copyright 2012 Jun Wako <wakojun@gmail.com>
+
+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
+
+#define VENDOR_ID       0xFEED
+#define PRODUCT_ID      0x6512
+#define DEVICE_VER      0x0001
+#define MANUFACTURER    QMK
+#define PRODUCT         XT keyboard converter
+#define DESCRIPTION     convert XT keyboard to USB
+
+
+/* matrix size */
+#define MATRIX_ROWS 16  // keycode bit: 3-0
+#define MATRIX_COLS 8   // keycode bit: 6-4
+
+/* key combination for command */
+#define IS_COMMAND() ( \
+    keyboard_report->mods == (MOD_BIT(KC_LSHIFT) | MOD_BIT(KC_RSHIFT)) || \
+    keyboard_report->mods == (MOD_BIT(KC_LCTRL) | MOD_BIT(KC_RSHIFT)) \
+)
+
+
+//#define NO_SUSPEND_POWER_DOWN
+
+/*
+ * XT Pin interrupt
+ */
+#define XT_CLOCK_PORT  PORTD
+#define XT_CLOCK_PIN   PIND
+#define XT_CLOCK_DDR   DDRD
+#define XT_CLOCK_BIT   1
+#define XT_DATA_PORT   PORTD
+#define XT_DATA_PIN    PIND
+#define XT_DATA_DDR    DDRD
+#define XT_DATA_BIT    0
+#define XT_RST_PORT    PORTB
+#define XT_RST_PIN     PINB
+#define XT_RST_DDR     DDRB
+#define XT_RST_BIT     7
+
+/* hard reset: low pulse for 500ms and after that HiZ for safety */
+#define XT_RESET() do { \
+    XT_RST_PORT &= ~(1<<XT_RST_BIT);  \
+    XT_RST_DDR  |=  (1<<XT_RST_BIT);  \
+    _delay_ms(500);                   \
+    XT_RST_DDR  &= ~(1<<XT_RST_BIT);  \
+} while (0)
+
+/* INT1 for falling edge of clock line */
+#define XT_INT_INIT()  do {    \
+    EICRA |= ((1<<ISC11) |      \
+              (0<<ISC10));      \
+} while (0)
+/* clears flag and enables interrupt */
+#define XT_INT_ON()  do {      \
+    EIFR  |= (1<<INTF1);        \
+    EIMSK |= (1<<INT1);         \
+} while (0)
+#define XT_INT_OFF() do {      \
+    EIMSK &= ~(1<<INT1);        \
+} while (0)
+#define XT_INT_VECT    INT1_vect