Merge pull request #324 from stan-dev/hotfix/v2.0.1

Hotfix/v2.0.1
Merge pull request #461 from stan-dev/release/v2.1.0

Release/v2.1.0
Merge branch 'master' of https://github.com/stan-dev/stan into hotfix/v2.1.1
Merge branch 'hotfix/v2.1.1' of https://github.com/stan-dev/stan into hotfix/v2.1.1
fixed leak on log_softmax, added brittle test; added code doc to softmax test
got rid of extraneous print in log_softmax test