add hhkb bluetooth functionality (rn42) (#2693)

* add hhkb bluetooth functionality (rn42)

pretty much straight from tmk

some minor changes to make things work

* hhkb jp personal keymap

* Revert "hhkb jp personal keymap"

This reverts commit 886713d8bb98572f03110f285706a8140a083892.

keyboards/hhkb/rn42/battery.h

@@ -0,0 +1,35 @@
+#ifndef POWER_H
+#define POWER_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef enum {
+    FULL_CHARGED,
+    CHARGING,
+    DISCHARGING,
+    LOW_VOLTAGE,
+    UNKNOWN,
+} battery_status_t;
+
+typedef enum {
+    LED_CHARGER = 0,
+    LED_ON,
+    LED_OFF,
+    LED_TOGGLE,
+} battery_led_t;
+
+/* Battery API */
+void battery_init(void);
+void battery_led(battery_led_t val);
+bool battery_charging(void);
+uint16_t battery_voltage(void);
+battery_status_t battery_status(void);
+
+#define BATTERY_VOLTAGE_LOW_LIMIT       3500
+#define BATTERY_VOLTAGE_LOW_RECOVERY    3700
+// ADC offset:16, resolution:5mV
+#define BATTERY_ADC_OFFSET              16
+#define BATTERY_ADC_RESOLUTION          5
+
+#endif