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

...Normal, and Uniform
The documentation should probably include which parameters and in what order they are returned, as:
  1. I believe that returning a single value (for this distribution) and multiple values (for distributions with multiple parameters) would be more clear from a "self-documenting code" point of view; however,
  2. Using specific return values means it would be impossible for clients to use an interface that contains DLogProbDParam as it would be distribution specific as to its signature; however,
  3. I am ignorant of statistical uses for this function so I cannot gauge if number 2 would even be an issue.