vidjil-algo: release 2020.04

see #4268 (closed)

Preparation

• CHANGELOG
• New features are described in doc/vidjil-algo.md

Pipelines

https://gitlab.inria.fr/vidjil/vidjil/pipelines/140961

• prepare-release (oui, sur autre pipeline)
• valgrind-unit
• valgrind-functional
• multiple_tests
• benchmarks

Déploiement

• doc
• app (vidjil-next)
• app (vidjil)