Initial commit for distribution package. Contains Exponential, Laplace, Normal, and Uniform
Added capability for distributions to use an alternate source of random numbers
Removed allocation in DLogProbDParam and improved comments.
Changed Parameters and SetParameters to Marshal and Unmarshal slice. Added parameter maps
Fixed tests associated with Parameter change
Changed FitPrior to SuffStat and ConjugateUpdate. Updated tests.
Added TODO for improving ConjugateUpdate
Changed (Un)MarshalSlice to (Un)MarshalParameters to add additional safety. Added interface definition.
Added clarification comment to ParameterMarshaler that the order is fixed.
Merge pull request #4 from gonum/feature-dist

Initial commit for distribution package. Contains Exponential, Laplace, ...