normalize probability distribution
add plot method
make distribution an instance of MonadPlus (plus is not yet implemented)
initial implementation of transitions
add examples
Towards Bayesian Stuff
Format decimal places when probabilities are expressed as Doubles
File rename
Merge pull request #1 from hugoferreira/wip

Towards Bayesian Stuff
Implements the samples method of Distribution using the alias method.
Hide some unnecessary variables.
Remove repeated 'samples' definition after rebase.
Merge pull request #2 from jcazevedo/alias-method

Implement the 'samples' method of Distribution using the alias method
Merge branch 'wip'