Hi all, in working on input-coercion of scalar types passed in to
GraphQL operations, I need to know whether a parsed object is actually
one of the Booleans. Yes, I could write "input = true or: [ input =
false ]", but would prefer the same elegance provided by our other
type-testing methods like isString, isInteger, isFloat, isNil,
However, I noticed EToys had already implemented #isBoolean and didn't
want to overload it. The Etoys usage is in conjunction with querying
the "type" of another object, so renamed those to #isBooleanType.