doc: add kernel interface documentation

doc/kernel-interface.txt

@@ -0,0 +1,59 @@
+=== KERNEL TYPES ====
+
+kern_handle_t
+kern_status_t
+kern_txnid_t
+kern_clock_t
+kern_msg_t
+
+
+=== KERNEL ENUMS ====
+
+kern_status_t:
+	KERN_SUCCESS
+	KERN_BAD_HANDLE
+
+clockid_t:
+	CLOCK_REALTIME
+	CLOCK_MONOTONIC
+
+
+=== KERNEL STRUCTS ====
+
+kern_msg_t {
+	void *buf;
+	size_t len;
+	kern_handle_t *handles;
+	size_t nhandles
+}
+
+=== KERNEL OBJECTS ====
+
+port
+timer
+address_space
+page_buf
+task
+thread
+event
+
+=== KERNEL SYSTEM CALLS ====
+
+handle_close
+
+port_create
+port_publish
+port_connect
+
+msg_send
+msg_recv
+msg_read
+msg_write
+
+timer_create
+timer_arm
+
+clock_gettime
+
+task_get
+task_move_handle