Git internals

[yatho]

https://git-scm.com/docs/git-cat-file
https://git-scm.com/docs/git-hash-object
https://git-scm.com/docs/git-write-tree

https://git-scm.com/book/en/v2/Git-Internals-Plumbing-and-Porcelain#ch10-git-internals