Add CLI definitions; CLI restructure

cli/transform.d.ts

@@ -0,0 +1,11 @@
+/**
+ * Definitions for custom compiler transforms that can be applied with the `--transform` option.
+ * @module cli/transform
+ *//***/
+
+import { Parser } from "../src/parser";
+
+export interface Transform {
+  /** Called when parsing is complete, before a program is instantiated from the AST. */
+  afterParse(parser: Parser): void;
+}