Added protocol and records for coin toss distributions and examples as well.

Using schema to require the input to the prob function be
PersistentVector, which is the output of the sample function.
Completed a todo that eliminates code duplication in Distribution and updated examples accordingly.
updated comments
simplified probability function and changed comments
updated example
adding the beginnings of PGM support

This is not remotely done. I’ll need to refactor things.