Remove or explain mention of "ideal monad" from package introduction.

The first thing the user reads after clicking on this library is

> We represent the target language itself as an ideal monad supplied by the user

I find this a bit confusing because "ideal monad" doesn't seem to be a widely known concept in Haskell (unlike, say, "free monad"). The references I have found give more general category-theoretic explanations and are a bit hard to grasp. In Haskell terms, it seems that ideal monads have a "pure" constructor, but I'm not sure if there are other conditions.

If the conditions are easy to state, perhaps they should be used instead of the term "ideal monad".