updating version numbers to 2.5
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
release notes for 2.5.0
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/issue-1087-eigen-3.2.2
Merge branch 'develop' into feature/issue-1087-eigen-3.2.2
updated to Eigen, but getting error in math checks not throwing
nan test for check_pos_definite, singular value test fix
Merge pull request #1088 from stan-dev/feature/issue-1087-eigen-3.2.2

Fixes #1087. Feature/issue 1087 eigen 3.2.2