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 = .;→→       →       \