Libraries checklist

[osa1]

The Fir standard library should include types and functions for these:

• JSON encoding and decoding
• Stable (across versions) PRNG
• Random input generation
  Similar to QuickCheck's Arbitrary, but it shouldn't be a trait. Instead it should have combinators.
  (Maybe check out https://github.com/HypothesisWorks/hypothesis first.)
• Benchmarking
• Pretty printing combinators PPrint in the standard library.