added NaN test for Phi_approx
added NaN test for abs
added NaN test for bessel_first_kind
added NaN test for bessel_second_kind
added NaN test for binary_log_loss
added NaN test for binomial_coefficient_log
added NaN test for digamma
added unit test for distance; includes test for nan
added unit test for dot; includes test for nan
added unit test for dot_self; includes test for nan
added NaN test for exp2
added NaN test for falling_factorial
added NaN test for fma
added NaN test for gamma_p
added NaN test for gamma_q
Merge branch 'develop' into feature/issue-843-test-nan
added NaN test for if_else
added NaN test for inv
added NaN test for inv_cloglog
added NaN test for inv_logit