Support "records" in Podlang (#507)

* Support both integer and string keys in anchored keys

* Podlang parser support for records

* Validate record usage in Podlang

* Lower records to middleware

* Cross-module record imports

* Tidying

* Record entry name literal

* More tidying

* More tests, make sure qualified record literals are supported

* Use snake-case for record entry names

* Review feedback

src/middleware/operation.rs

@@ -860,8 +860,12 @@ impl fmt::Display for Operation {
 
 pub(crate) fn root_key_to_ak(root: &Value, key: &Value) -> Option<AnchoredKey> {
     let root_hash = Hash::from(root.raw());
-    key.as_str()
-        .map(|s| AnchoredKey::new(root_hash, Key::from(s)))
+    if let Some(s) = key.as_str() {
+        Some(AnchoredKey::new(root_hash, Key::from(s)))
+    } else {
+        key.as_int()
+            .map(|i| AnchoredKey::new(root_hash, Key::from(i)))
+    }
 }
 
 /// Returns the value associated with `output_ref`.