Toward its goal, this commit also:
* Adds a new section of logical functions, and defines `not`, `and`,
`or` for all current types.
* Extends `OneOf` choice/union type to allow argument types that are
themselves `OneOf` types.
* Adds a readable .toString() method for TypePatterns.
* Defines negate (as a no-op) and isnan (as always true) for the Undefined
type
* Extends comparisons to the Undefined type (to handle comparing vectors
of different lengths)
