feat: add clean function

Author: ttytm

src/lib.c.v

@@ -51,6 +51,7 @@ fn C.webui_set_position(win Window, x usize, y usize)
 fn C.webui_set_profile(win Window, name &char, path &char)
 fn C.webui_get_url(win Window) &char
 fn C.webui_navigate(win Window, url &char)
+fn C.webui_clean()
 
 // -- JavaScript ----------------------
 fn C.webui_run(win Window, script &char)

src/lib.v

@@ -234,6 +234,11 @@ pub fn (w Window) navigate(url string) {
 	C.webui_navigate(w, &char(url.str))
 }
 
+// clean frees all memory resources. Should be called only at the end.
+pub fn clean() {
+	C.webui_clean()
+}
+
 // == Javascript ==============================================================
 
 // run executes JavaScript without waiting for the response.