This just defines how these are parameterized, and doesn't provide any functionality. The list is also very incomplete at this point (I got tired of typing them in). However, it's a start. We can start filling method definitions for the pdf, cdf and sample functions, etc.
It happens that I was working on some of the functionality last evening. I will take what I did and put it in your framework.
You are using capitalized names for distributions, which I think is a good idea because it distinguishes such names as Logistic for the distribution and logistic for the function. I will stay with that convention unless someone shouts (I think Jeff prefers lower-case names)