Middleware improvements

Addresses #7 #10 #11 #13 

This should largely address the problems in the linked issues by incorporating a number of key changes:
- `pr-values` is reset to be a no-op, per @gfredericks suggestion.
- Whidbey now uses an internal function as a renderer, allowing it to use its own options and avoid altering the Puget defaults.
- The profile generated by Whidbey is namespaced and added to the list of active profiles using `merge-profiles` rather than trying to tack it onto the `repl` profile.
- Versions for Puget and Whidbey are pinned, rather than relying on `"RELEASE"`.