Support for properties of distributions

[haykam821]

Currently, discrete distributions support samples, where a specific value of a distribution is chosen at random. However, other stable properties of a distribution are also interesting and could be supported. For example, the mean of a d6 dice is 3.5. Other properties that could be supported include quantiles, the median, range, minimum, maximum, mode, variance, standard deviation, and skewness.

• [x] #284
• [ ] Quantiles
• [ ] Median
• [ ] Range
• [ ] #286
• [ ] Mode
• [ ] Variance/standard deviation
• [ ] Skewness

[haykam821]

I'm starting to work on some of these distribution properties, and I've already implemented mean, though the list of properties I gave in the issue body is probably too large for me to do in a single pull request. Would it make sense to split this issue into multiple issues so that I can correlate each issue to a pull request?

[printfn]

Up to you I suppose! I wouldn't worry too much about how you organise the PRs :)