Document relation order for current-typecheck-relation

[Alexis King]

For current-typecheck-relation, it would be nice if the documentation mentioned which of the two types is the “expected” type and which one is the “given” type.

[Alex Knauth]

The first one is always the given and the second one is always the expected. We should add this to the documentation for current-typecheck-relation, typecheck?, and typechecks?.

[Stephen Chang]

document relation order for current-typecheck-relation; closes #48

→ <<cset 896ec531510c>>