806: Implement hyper.rewrite(Sum)

This adds the function _eval_rewrite_as_Sum to the class hyper.
806: hyper.rewrite(Sum)

Change return value to Piecewise
Add tests
806: Improve code style
Hermite quadratic version to Mack's Linear version

Have reduced the time complexity involved in the hermite reduction (method) from m^2 to m-1 by using Mack's linear version instead of the quadratic function.
Also no partial fraction decomposition of f(input function )or square-free factorization of its denominator is required decreasing the time complexity further
Add Chetna Gupta to the AUTHORS/aboutus/.mailmap. Welcome to SymPy!
fix test_import dir dependency
fix Sum and Product _eval_subs
3785: rework multiplicity and handling in log
Skeleton for elliptic integrals
major rewrite of pull #1408:

    * change names
    * docstrings
    * some documentation
    * mpmath translations
    * eval(), fdiff(), some rewrite methods
Added tests for elliptic integrals
This is still in implementation phase, i am trying to workout integration
of trignometric functions of the form tan(x), which would call
integrate_hypertangent_reduce and integrate_hypertangent_polynomial
To get this working i need coupledDifferntialSystem which still stands TODO