Merge branch 'develop' of https://github.com/stan-dev/stan into develop
compiler warnings: removed warning from fwd abs
Merge pull request #1035 from stan-dev/feature/issue-1034-compiler-warnings

Fixes #1034. compiler warnings: removed warning from fwd abs
Merge branch 'feature/issue-771-ode-solver' of https://github.com/stan-dev/stan into feature/issue-771-ode-solver
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/issue-771-ode-solver
Merge branch 'develop' into feature/issue-771-ode-solver
cleaned up header guards, removed diff of integrator solver and links