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.
added std::vector version of check_ordered with tests
Merge pull request #933 from stan-dev/feature/issue-891-check-ordered-nan

Feature/issue 891 check ordered nan