Updates to environment v1

Contains most of the minor changes to V1, like updating signatures. No new big features.

Includes:

• !107 (merged)
• !43 (merged)
• !93 (merged)
• !94 (merged)
• !234 (merged)
• !98 (merged)
• part of !281
• add nothing of !96 (merged) (decided to not add first_some)
• add !135 (merged)
• add !162 (merged) (partly done, added Z.pp_print rather than Z.pp for compatibility with original z.mli)
• add !165 (merged) (completely reworked)
• add !212 (merged)
• add !254 (merged)
• clean history

The MR updates existing signatures, removes deprecated ones (option, mbytes) and adds new ones (Z, char). Signatures are as much as possible a verbatim subset of the original file, they are now easy to review simply using a diff tool.

Reviewers: @mbouaziz @raphael-proust @sribar
Coverage: 35202/51217 (68.73%)