Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
updating artifacts to v2.4.0
release notes for Stan C++ 2.4
Merge branch 'develop' into feature/issue-781-v2.4.0
updating doc to right date
Merge pull request #784 from stan-dev/feature/issue-781-v2.4.0

Fixes #781. Feature/issue 781 v2.4.0
Merge branch 'develop' into feature/issue-362-ensemble-samplers