Split repo documentation

The repo documentation targets both repo users (devs, test, api) and duniter users (api/manual, user). The duniter user documentation should be moved to duniter website repo and adapted for the public of duniter:

• https://duniter.org/wiki/duniter-v2/ for technical public
• https://duniter.org/wiki/g1v2/ for general public

changed milestone to %runtime-802

added C-doc label

assigned to @HugoTrentesaux

changed milestone to %runtime-803

changed milestone to %client-0.9.0

The current strategy is to have the repo be more focused on auto-generated documentation.

changed milestone to %client-0.10.0

mentioned in merge request !290 (merged)

mentioned in merge request !306 (merged)

closed with merge request !306 (merged)