Initial event manager work, and two first events.

* Add initial event manager implementation,
  roughly mimicking Nordic's API.
* Add `position_state_changed` and
  `keycode_state_changed` events.
* Hook up HID and keymap to new events
  instead of using behaviour global event
  crazy.

app/include/linker/zmk-events.ld

@@ -0,0 +1,16 @@
+#include <linker/linker-defs.h>
+
+	SECTION_PROLOGUE(event_types,,)
+	{
+        	__event_type_start = .; \
+        	KEEP(*(".event_type")); \
+        	__event_type_end = .; \
+	} GROUP_LINK_IN(ROMABLE_REGION)
+
+        SECTION_PROLOGUE(event_subscriptions,,)
+	{
+        	__event_subscriptions_start = .; \
+        	KEEP(*(".event_subscription")); \
+        	__event_subscriptions_end = .; \
+	} GROUP_LINK_IN(ROMABLE_REGION)
+

app/include/linker/zmk-linker-defs.h

@@ -0,0 +1,6 @@
+
+
+#define→EVENT_TYPE_SECTIONS()→  →       →       →       \
+→       →       __event_type_start = .;→      →       \
+→       →       KEEP(*(".event_type_*"));→    →       \
+→       →       __event_type_end = .;→→       →       \

app/include/zmk/event-manager.h

@@ -0,0 +1,65 @@
+#pragma once
+
+#include <stddef.h>
+#include <kernel.h>
+#include <zephyr/types.h>
+
+struct zmk_event_type
+{
+    const char *name;
+};
+
+struct zmk_event_header {
+    const struct zmk_event_type* event;
+};
+
+typedef int (*zmk_listener_callback_t)(const struct zmk_event_header *eh);
+struct zmk_listener
+{
+    zmk_listener_callback_t callback;
+};
+
+struct zmk_event_subscription {
+    const struct zmk_event_type *event_type;
+    const struct zmk_listener *listener;
+};
+
+#define ZMK_EVENT_DECLARE(event_type) \
+    struct event_type* new_##event_type(); \
+    bool is_##event_type(const struct zmk_event_header *eh); \
+    const struct event_type* cast_##event_type(const struct zmk_event_header *eh); \
+    extern const struct zmk_event_type zmk_event_##event_type;
+
+#define ZMK_EVENT_IMPL(event_type) \
+    const struct zmk_event_type zmk_event_##event_type = { \
+        .name = STRINGIFY(event_type) \
+    }; \
+    const struct zmk_event_type* zmk_event_ref_##event_type __used __attribute__((__section__(".event_type"))) = &zmk_event_##event_type; \
+    struct event_type* new_##event_type() { \
+        struct event_type* ev = (struct event_type *) k_malloc(sizeof(struct event_type)); \
+        ev->header.event = &zmk_event_##event_type; \
+        return ev; \
+    }; \
+    bool is_##event_type(const struct zmk_event_header *eh) { \
+        return eh->event == &zmk_event_##event_type; \
+    }; \
+    const struct event_type* cast_##event_type(const struct zmk_event_header *eh) {\
+        return (const struct event_type*)eh; \
+    };
+    
+
+#define ZMK_LISTENER(mod, cb) \
+    const struct zmk_listener zmk_listener_##mod = { \
+        .callback = cb \
+    };
+
+#define ZMK_SUBSCRIPTION(mod, ev_type) \
+    const Z_DECL_ALIGN(struct zmk_event_subscription) _CONCAT(_CONCAT(zmk_event_sub_,mod),ev_type) __used __attribute__((__section__(".event_subscription"))) = { \
+        .event_type = &zmk_event_##ev_type, \
+        .listener = &zmk_listener_##mod, \
+    };
+
+#define ZMK_EVENT_RAISE(ev) \
+    zmk_event_manager_raise((struct zmk_event_header *)ev);
+
+int zmk_event_manager_raise(struct zmk_event_header *event);

app/include/zmk/events/keycode-state-changed.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <zephyr.h>
+#include <zmk/event-manager.h>
+
+struct keycode_state_changed {
+    struct zmk_event_header header;
+    u8_t usage_page;
+    u32_t keycode;
+    bool state;
+};
+
+ZMK_EVENT_DECLARE(keycode_state_changed);

app/include/zmk/events/position-state-changed.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include <zephyr.h>
+#include <zmk/event-manager.h>
+
+struct position_state_changed {
+    struct zmk_event_header header;
+    u32_t position;
+    bool state;
+};
+
+ZMK_EVENT_DECLARE(position_state_changed);