- Added MLE for 'Gamma' distribution.
- Added log-probability and log-density to all distributions.
- Added a method for sampling a single value from a distribution, see
'BaseDistribution.random'. - Changed the observation label in 'DiscreteDistribution' from ~n to ~k.
- Bumped minimum required ocaml-gsl version to 1.14.0 and dropped custom
'Combi' stubs.