concept: move rsx out to its own crate

packages/rsx/src/errors.rs

@@ -0,0 +1,15 @@
+macro_rules! missing_trailing_comma {
+    ($span:expr) => {
+        proc_macro_error::emit_error!($span, "missing trailing comma")
+    };
+}
+
+macro_rules! attr_after_element {
+    ($span:expr) => {
+        proc_macro_error::emit_error!(
+            $span,
+            "expected element";
+            help = "move the attribute above all the children and text elements"
+        )
+    };
+}