Enhancement of Statistics Module

Currently the stats module lacks some useful features as suggested on the ideas page, like Random Walks, Random Matrices, etc. There is also a scope of completing the work of GSoC 2018 by Akash Vaish like, exporting expressions of random variables to external libraries. There are also certain issues with results being produced by various functions and methods, like, sometimes unwanted complex results are produced for simple probability expressions or, unevaluated results are given as output. I would divide my project into the following broad categories:

1. Implementing additional multivariate distributions.
2. Implementing Markov Chains, Random Walks, Bernoulli Process(extending PR #15058), and Poisson Process.
3. Implementing Random Matrices.
4. Implementing mechanism to export random variables to PyStan, PyMC3, NumPy, etc.
5. Adding support for assumptions of dependence among random variables.
6. Adding support to enhance result generation by statistics module.