create accessors for all distributions

[bentheiii]

Some distributions have this (like Exp), but others (like LogNormal) don't.

for example:

impl LogNormal {
  pub fn location(&self)->f64 { self.location }
  pub fn scale(&self)->f64 { self.scale }
}

this will make it far easier to interoperate these distributions in a variety of ways.

[YeungOnion]

Those without parameter getters

• Dirac
• DiscreteUniform
• LogNormal
• Triangular
• Uniform

[Qazalbash]

I'd like to contribute by adding this feature. Any important guidelines or considerations before I start?

[YeungOnion]

Hi, thanks for finding a place to contribute!

Some considerations; I believe they are relevant mostly to the multivariate distributions (we may not have consistency on these yet):

• it is Rust idiom to not include the word get for these kinds of functions
• non-Copy fields should not clone for immutable accessor, clones should be opt-in by caller