2.1.0

CHANGES:

• Add the constant combinator, typically used to tag objects.
• Add the null combinator.
• Add obj0 (matches any object) and empty (matches the empty object)
  combinators.
• Add the union combinator.
• Add the dft field combinator.
• Add the json combinator.
• Add the enum combinator.
• Add the satisfies combinator.
• Add the tupN combinators family (tup1 to tup10).