Add dists summary stats (#290)

* Added summary statistics to the distributions  (#287)

* added the mean and variance for the uniform dist along with a test for both

* i added fixes to the mean and var test as i forgot to run the test before hand

* added a mean and var for determenistic dist and a test for it that passes

* found a 'better' (i hope) way to do the mean and var for uniform and deterministic so changed the code

* added a mean and var for triangular also added a test

* Created mean and var for gamma and made a test

* added mean and var for exp along with a test

* added mean and and var for weidbull along side a test also imported math to make calculations smoother rather than using np

* added mean and and var for empirical and a test

* added mean and and var for PMF and a test

* added mean and and var for sequential and a test

* added mean and and var for poisson and a test

* added mean and and var for geometric and a test

* added mean and and var for phase type and a test alos imported numpy

* added mean and and var for erlang and a test

* added mean and and var for hyper exp and a test

* added mean and and var for hyper erlang and a test

* added mean and and var for coxian and a test

* added the ability to find mean and var for dists V1 (no test but works in practice)

* added version 2 of the mean and var grabber that is cleaner

* added a mean and var for normal + a test

* added coxian mean and var (already had tests not sure where it went maybe when i lost the file) previous test still works

* added mean and var for lognormal + a test

* added mean and var for normal (trun)

* added mean and var for poisson interval no test (but it works on ciw its self)

* added mean and var for mixture + test

* added mean and var for combined + test

* disabled the print of the mean and var summary but keot the code for now

* started to add sd mean and range but forgot to push every change but done test for them all, ive done combined, uniform , det ,triangular, exp, gamma, normal ,lognormal , weibull, empirical ,sequential

* added pmf ,sd ,range and a test

* added sd mean range of pahse which Erlang / HyperExponential / HyperErlang / Coxian inherit

* added sd med range for poissoninterval

* added sd , med and range for poisson

* added sd , med and range for  binomial and mixture

* fixed negative sqrt prob when dealing with negative var

* added some small changes to imports and to triangular

* quick clean up adding some context to my code

* changed mean and var for hyper erlang

* made changes to improve coverage 24 lines to 12

* coverage down from 12 to 6 lines

* coverage lines missed from 6 to 3

* Coverage is now 100% except for a deliberate missed line with unrun code.

* small clean up removing some blank lines and some wasted text

* removed print code

* here is the updated version from the overhall that created some errors

* added test to uniform to see if sample mean == to theoretical mean

* some small cleanups

* tidy up some lines, tests, merge some tests

* use statistics library instead of scipy

* use statistics library instead of scipy in tests

* remove supurfluous lines in tests

* add docs, add limits for adding distributions

* fix duplicate label in docs

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Co-authored-by: ioanb16 <barberioan6@gmail.com>

Author: geraintpalmer