CHANGES:
- Remove unused code from test setup (!4 - @hannesm)
- BUG FIX: of_octets: create ring buffer earlier to avoid missing data (!5 - @hanensm, review by @dinosaure @reynir)
- Add function
commit : t -> Digestif.SHA1.t option
(!6 !8 - @hannesm @reynir, review by @dinosaure)