Feature/log cdf log ccdf

This pull request adds (vectorized and using operands_and_partials) cdf_log and ccdf_log to all univariate continuous distributions (except trunc normal) and all univariate discrete distributions (except hypergeometric and ordered logistic). All cdf and logprob funcitons for all distributions were also vectorized (if not already) and now use operands_and_partials. gamma_p and gamma_q (lower and upper normalized incomplete gamma functions) were added to the math and autodiff lib.