Implement module loading and imports

examples/import/main.dcdl

@@ -0,0 +1,6 @@
+let
+  schema = import "./schema.dcdl";
+in
+  schema.MyConfig & {
+    host = "localhost";
+  }

examples/import/schema.dcdl

@@ -0,0 +1,4 @@
+MyConfig = {
+  host = String;
+  port = Int & > 443 default 8080;
+};