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
Merging

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
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
fixed #1160 by using arena for precomputed_gradients storage
Merge branch 'develop' into bugfix/feature-1160-memory-leak
removed unused vector<vari*> ctor from precomputed_gradients
added in/out labels on doc for parameters
Merge pull request #1168 from stan-dev/bugfix/feature-1160-memory-leak

Fixes #1160. Bugfix/feature 1160 memory leak