🛐 Worship the OCaml module system

[jonsterling]

This pull request contains two changes:

1. Replace the handler records with modules. I found (experimentally) while hacking algaett that it is a lot less painful to program the handlers with modules than it is to write out the records. Features like include and open are useful, and I would not discount reducing the stress of being several parenthesis/brace delimiter levels into a gnarly piece of code.

2. I have refactored the modules so that the main signatures are declared (and documented) just once. This removes a lot of duplication that is annoying when refactoring code. It also means that if documentation is generated for the private/internal modules, the documentation comments will appear for these as well. Sometimes we wish to expose a different public interface than the private interface (but I didn't notice that in this library); that too can be incorporated, through judicious use of include.

Let me know if you have any feedback about these changes, or if you don't like it for some reason. Thanks!

[favonia]

Just wanted to add that, under the records=modules Thought, these two approaches should be isomorphic. I hope we can fix this problem at least in the languages/tools we created. :-)