Merge all the chell-* subprojects into one repo (2 of 3)

Add 'chell-quickcheck/' from commit '91466759f3d793c5117db37a490c87f8deacfafd'

git-subtree-dir: chell-quickcheck
git-subtree-mainline: 090aecd3ae3aae5145ee484ceb1f7404fb827c41
git-subtree-split: 91466759f3d793c5117db37a490c87f8deacfafd
tree: f4dd7233385feb85f8b3befa61e901ee5b5e8e74
  1. chell-quickcheck/
  2. chell/
  3. license.txt