Holomorphy

[Tragicus]

Motivation for this change

Resurrection of https://github.com/math-comp/analysis/pull/204.

fyi: @mkerjean

Checklist

• [x] added corresponding entries in CHANGELOG_UNRELEASED.md

• [x] added corresponding documentation in the headers

Reference: How to document

Merge policy

As a rule of thumb:

• PRs with several commits that make sense individually and that all compile are preferentially merged into master.
• PRs with disorganized commits are very likely to be squash-rebased.

Reminder to reviewers

• Read this Checklist
• Put a milestone if possible
• Check labels

[Tragicus]

What should I do about the lemmas I put in unstable.v that require real-closed?