Add some more ideas

I was thinking today about how the | operator is way briefer than
writing a comprehension in a collection, but writing the comprehension
is nice to format and | is awkward. Also when writing down the type of
the | operator ... it's a challenge (also to typecheck it).

Perhaps, adding a spread/unpack operator will resolve both issues. It
would be slightly more verbose, but not terribly so. And I believe it
would be more readable too.

ideas/roadmap.md

@@ -1,5 +1,9 @@
 # Roadmap
 
+## In progress
+
+ * Type system.
+
 ## Near term
 
  * Accept an expression through `--expr` for `rcl evaluate`.
@@ -14,10 +18,13 @@
  * Absorb the `highlight` command into `fmt` and make it use the same coloring?
  * Evaluate whether to add a tuple type to describe heterogeneous lists of
    statically known length.
+ * Add a spread operator for inside collections, and evaluate whether it should
+   supersede the dict/set union operator. It would solve some typing issues, and
+   it's easier to format in a pleasant way.
+ * Add nested fields to record syntax, i.e. `{x.y = "z"} == {x = {y = "z" }}`.
 
 ## Long-term
 
- * Type system.
  * Add a more efficient runtime system, possibly with a garbage collector.
  * Multithreaded evaluation. Due to strict evaluation and being purely
    functional without side effects, this is actually feasible: when we evaluate