One Dimensional Marginal Constructor

[akleeman]

Adds a constructor for a MarginalDistribution to make it easier to create one dimensional distributions.

Ie, now you can do:

MarginalDistribution(10.0, 0.1);

instead of

MarginalDistribution(Eigen::VectorXd::Constant(1, 10.0),
                     Eigen::VectorXd::Constant(1, 0.1));

[jbangelo]

I love one dimensional data structures!