Use enum wl_keyboard_key_state instead of integer

Instead of using a uint32_t for state everywhere (except on the wire,
where that's still the call signature), use the new
wl_keyboard_key_state enum, and explicit comparisons.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/clients/resizor.c b/clients/resizor.c
index 8186561..d02ab29 100644
--- a/clients/resizor.c
+++ b/clients/resizor.c
@@ -139,12 +139,13 @@
 
 static void
 key_handler(struct window *window, struct input *input, uint32_t time,
-	    uint32_t key, uint32_t sym, uint32_t state, void *data)
+	    uint32_t key, uint32_t sym, enum wl_keyboard_key_state state,
+	    void *data)
 {
 	struct resizor *resizor = data;
 	struct rectangle allocation;
 
-	if (state == 0)
+	if (state == WL_KEYBOARD_KEY_STATE_RELEASED)
 		return;
 
 	window_get_allocation(resizor->window, &allocation);