Add support for module-level and crate-level attributes

rr_frontend/case_studies/tests/src/enums.rs

+#![rr::import("refinedrust.extra_proofs.tests.enums", "enums")]
+
+enum Option<T> {
+    None,
+    Some(T)
+}
+
+impl<T> Option<T> {
+    pub fn none() -> Self {
+        Self::None
+    }
+
+    pub fn some(x : T) -> Self {
+        Self::Some(x)
+    }
+}
+
+//#[repr(usize)]
+#[rr::refined_by("sizes")]
+enum sizes {
+    #[rr::pattern("Sz1")]
+    #[rr::variant("()")]
+    Sz1,
+    #[rr::pattern("Sz2")]
+    #[rr::variant("()")]
+    Sz2,
+}
+
+impl sizes {
+    #[rr::returns("Sz1")]
+    pub fn new() -> Self {
+        Self::Sz1
+    }
+}