Camera-ready version for CPP 2020

Address reviewer comments; update mathlib.

Independence of CH

Submitted version for CPP 2020; improvements since v2.0

snapshot-2019-10

Version of flypitch up to date with mathlib's snapshot-2019-10.

Independence of CH

A formal proof of the independence of the continuum hypothesis.

Unprovability of CH

Contains a complete verification of the unprovability of the continuum hypothesis from ZFC.