Merge branch 'develop' of https://github.com/stan-dev/stan into develop
added update to makefile for eigen asserts and fixed three tests
added failing tests
fixed check_corr_matrix for nan inputs
Merge branch 'feature/issue-891-check-symmetric-nan' into feature/issue-891-check-corr-matrix-nan
added doc in code for check_corr_matrix
updating test for check_simplex_test so it passes with EIGEN_NO_DEBUG
fix factorU test
updating bfgs_update test
fix bfgs update test
Merge branch 'bugfix/issue-904-eigen-assert-bugs' of https://github.com/stan-dev/stan into bugfix/issue-904-eigen-assert-bugs
added NaN test for check_greater
added doc in code for check_greater
added NaN test for check_greater_or_equal
added doc in code for check_greater_or_equal
added NaN test for check_less
added doc in code for check_less
added NaN test for check_less_or_equal
added doc in code for check_less_or_equal
added NaN test for check_nonnegative