Merge branch 'develop' of https://github.com/stan-dev/stan into feature/vari-delete-fix
add no-op virtual delete() method to chainable() so that ctor exceptions can be cleaned up without seg faulting
Merge pull request #76 from stan-dev/feature/vari-delete-fix

Add delete method to chainable to allow exceptions in vari ctors
Merge branch 'develop' into gp_improvements