Track doc comments and render them in :doc

tests/functional/repl/doc-comments.nix

@@ -0,0 +1,57 @@
+{
+  /**
+    Perform *arithmetic* multiplication. It's kind of like repeated **addition**, very neat.
+
+    ```nix
+    multiply 2 3
+    => 6
+    ```
+   */
+  multiply = x: y: x * y;
+
+  /**👈 precisely this wide 👉*/
+  measurement = x: x;
+
+  floatedIn = /** This also works. */
+    x: y: x;
+
+  compact=/**boom*/x: x;
+
+  /** Ignore!!! */
+  unambiguous = 
+    /** Very close */
+    x: x;
+
+  /** Firmly rigid. */
+  constant = true;
+
+  /** Immovably fixed. */
+  lib.version = "9000";
+
+  /** Unchangeably constant. */
+  lib.attr.empty = { };
+
+  lib.attr.undocumented = { };
+
+  nonStrict = /** My syntax is not strict, but I'm strict anyway. */ x: x;
+  strict = /** I don't have to be strict, but I am anyway. */ { ... }: null;
+  # Note that pre and post are the same here. I just had to name them somehow.
+  strictPre = /** Here's one way to do this */ a@{ ... }: a;
+  strictPost = /** Here's another way to do this */ { ... }@a: a;
+
+  # TODO
+
+  # /** This returns a documented function. */
+  # documentedArgs =
+  #   /** x */
+  #   x:
+  #   /** y */
+  #   y:
+  #   /** x + y */
+  #   x + y;
+
+  # /** Documented formals */
+  # documentedFormals = 
+  #   /** x */
+  #   x: x;
+}