added autodiff tests for mean, min,minus,mult_lower_transpose
added appropriate includes for agrad tests
added autodiff tests for operators
added more autodiff tests for prod,rep_matrix,rep_vector,rep_row_vec,row,rows
added autodiff tests to rows_dot_prod,rows_dot_self,sd,softmax
added autodiff tests for sort,sum,tcrossprod,to_fvar,to_vector
added autodiff tests for trace,transpose,variance
added 3rd deriv tests for abs, acos, acosh, asin,asinh,atan,atan,atanh
added 3rd deriv tests for bessel1,bessel2,binary_log_loss,cbrt,ceil,cosh,cos,digamma
added 3rd deriv tests for erf, erfc,exp,exp2,expm1,fabs,falling_factorial,fdim,floor,fma,fmax,fmin,fmod
added more 3rd deriv autodiff tests
added 3rd deriv autodiff tests for lmgamma,log10,log1mexp,log1minvlogit,log1m,log1p_exp,log1p,log2,log,logit,mod bessel functions,mult_log
added 3rd deriv autodiff tests for operators
added third deriv autodiff tests to rest of functions