added NaN test for acosh
updated nan test for acosh
updated agrad/fwd/acosh
added NaN tests for agrad/fwd/acosh
fixed NaN bug in agrad/rev/acosh and switched to no namespace version of acosh
updated bound tests for acosh
added NaN and derivative doc for acosh in manual
added NaN test for bessel_first_kind
added NaN tests for agrad/bessel_first_kind
added NaN and derivative doc for bessel_first_kind in manual
added NaN test for bessel_second_kind
added NaN tests for bessel_second_kind
added NaN and derivative doc for bessel_second_kind to manual
switched to no namespace version of cbrt
added NaN tests for cbrt
added NaN and derivative doc for cbrt to manual
added NaN test for ceil
add failing NaN test for ceil
fixed NaN gradient for ceil using unlikely()
added NaN test for ceil