Squashed 'deps/cereal/' content from commit 7121e91

git-subtree-dir: deps/cereal
git-subtree-split: 7121e91e6ab8c3e6a6516d9d9c3e6804e6f65245
Merge commit 'ffda91fed6894916d978ff49338deb03f647a857' as 'deps/cereal'
Added cereal serialization library