Math.NET behaviour for INFINITY values

[troublescooter]

What is the reason for adopting this odd behaviour? It seems to me that the most sensible thing to do would be to return 0 if shape isn't NaN or (+-)INFINITY. This is just one instance, as there seem to be a couple of other odd return values.

    impl Mean<f64> for Gamma {
    /// Returns the mean of the gamma distribution
    ///
    /// # Remarks
    ///
    /// Returns `shape` if `rate == f64::INFINITY`. This behavior
    /// is borrowed from the Math.NET implementation
    ///
    /// # Formula
    ///
    /// ```ignore
    /// α / β
    /// ```
    ///
    /// where `α` is the shape and `β` is the rate

[boxtown]

A lot of these as indicated by the doc-string were borrowed behavior from Math.NET but I agree that not all of this behavior is necessarily correct. Looking through the commits of the Math.NET source I don't see a good reason for this particular method to not return 0, I'm happy to accept any PRs addressing this and other odd behavior you've seen

[troublescooter]

Fixed in #116