analysis: add check of composite types (structs and enums)

- analysis: add bool check for loop condition exprs

examples/hello.ry

@@ -17,8 +17,13 @@ enum B {
     c
 }
 
+enum C {
+    blah
+    bluh
+}
+
 fn test_function() B {
-    return B.a;
+    return B.bluh;
 }
 
 fn multwo(num: i32, double_flag: bool) i32 {