Remove dependencies on yf for yT.
Clean up yT comments and try to standardize descriptor description terminology.
Allow specifying a constructor _or_ a parent prototype as the parent argument to yT. Similarly allow specifying a constructor _or_ a specific instance to defineProperty and defineProperties.
Chainable data descriptors are marked writable by default; a chainable non-writable descriptor doesn't really make sense.
Non-owned  values are sufficient to consider something a data descriptor, as with Object.create et al.