added cdf_log test to distribution test_fixture
added cdf_log to normal distribution with test
vectorized exponential_cdf and added missing test
added cdf_log to exponential with test
added cdf_log with test for cauchy distribution
added cdf_log to beta distribution with test
added vectorized cdf to double exponential with test
added vectorized cdf_log to double exponential with test
vectorized cdf and use operands_and_partials for exp_mod_normal distr
added cdf_log to exp_mod_normal
added operands_and_partials to gumbel cdf
added cdf_log to gumbel distribution
added cdf_log to inv_chi_square distr
added cdf_log to inv_gamma distr
added cdf_log to logistic distr
added operands_and_partials to cdf for lognormal
added cdf_log to lognormal distr
added operands_and_partials to cdf of normal distr
added cdf_log to pareto distr
added cdf_log to scaled_inv_chi_square