This has involved quite a bit of reorganisation and some improvements in
resugaring so that the results look nice. In summary:
* Expression search now gives back a RawImp rather than a checked term,
which allows it to include case expressions
* Case with one pattern is resugared to a destructuring let
* Some name generation issues address in function generation
We look at intermediate results for local variables which are functions
that return a concrete type, or recursive calls that return a single
constructor type. In these cases, we:
* let bind the local variable/recursive call
* generate a new definition for the scope, as a 'case' function
When we recursively generate the definition, it's a bit more restricted
so as not to explode the search space. We only take the first result, we
only look one constructor deep, and we go right to left on variable
splitting so only deconstruct the name we've just added.
