• Math::BigFloat madness workaround, see
  http://blog.schmorp.de/2016-04-23-mathbigfloat-maintainer-fail.html
  (bugreport by zdm@softvisio.net).
  
• add text_keys and text_strings options to force CBOR text encoding
  for perl hash keys or all strings, as a result of discussions
  with Fredrik Ljunggren.
  
• implement support for arbitrary-exponent numbers (see
  http://peteroupc.github.io/CBOR/bigfrac.html, tags 264 and 265)
  for both en- and decoding.
  
• implement support for rational numbers (see
  http://peteroupc.github.io/CBOR/rational.html, tag 30) for both
  en- and decoding.
  
• the above effectively implements all registered CBOR extensions
  in a sensible manner.
  
• remove some weird dead code that was duplicated (%FILTER).
  
• add t/58hv.t, which tests hashes and the new text* flags.
  hashes apparently were not encoded at all in any of the existing
  tests.
  
• document Math::BigFloat base-2 performance/crash issues.
  
• use stability canary.