0.0.1.dev8 (from datatest 0.9.4)

• Added Python 3.8 testing and support.
• Added Predicate class to formalize behavior--also provides inverse-matching
  with the inversion operator (~).
• Added new methods to Query class:
  • Added unwrap() to remove single-element containers and return their
    unwrapped contents.
  • Added starmap() to unpack grouped arguments when applying a function
    to elements.