added NaN test for check_ordered
added doc in code for check_ordered
added NaN test for check_square
added doc in code for check_square
Revert "added doc in code for check_square"

This reverts commit 26ce674ac72aa39be2208062c4bc83c2d823ceef.
Revert "added NaN test for check_square"

This reverts commit 525526e2104caae15d73aee7edd27f5f60cc3255.
updated solve_ode finite difference testing framework
stash
Merge branch 'feature/issue-771-ode-solver' of https://github.com/stan-dev/stan into feature/issue-771-ode-solver
remove unused function in test/unit/math/ode/util
updated solve_ode using nested gradient calls
consolidated solve_ode testing framework
added std::vector version of check_ordered with tests
Merge branch 'feature/issue-891-check-ordered-nan' into feature/issue-771-ode-solver
added error_checks with tests to solve_ode