Support setting referent properties via attributes (#843)

Co-authored-by: Kenneth Loeffler <kenloef@gmail.com>

src/rojo_ref.rs

@@ -0,0 +1,30 @@
+use std::{fmt, sync::Arc};
+
+use serde::{Deserialize, Serialize};
+
+pub const REF_ID_ATTRIBUTE_NAME: &str = "Rojo_Id";
+pub const REF_POINTER_ATTRIBUTE_PREFIX: &str = "Rojo_Target_";
+
+// TODO add an internment strategy for RojoRefs
+// Something like what rbx-dom does for SharedStrings probably works
+
+#[derive(Debug, Default, PartialEq, Hash, Clone, Serialize, Deserialize, Eq)]
+pub struct RojoRef(Arc<String>);
+
+impl RojoRef {
+    #[inline]
+    pub fn new(id: String) -> Self {
+        Self(Arc::from(id))
+    }
+
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        self.0.as_str()
+    }
+}
+
+impl fmt::Display for RojoRef {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.as_str())
+    }
+}