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
Merge pull request #2032 from katjasophie/806_hyper.rewrite(Sum)

Issue 806: Implement hyper.rewrite(Sum)
Update Raoul in the .mailmap file
Merge branch 'master' of github.com:sympy/sympy
fix Sum and Product _eval_subs
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
Merge pull request #1948 from cheatiiit/hermite

Hermite quadratic version to Mack's Linear version
Add Chetna Gupta to the AUTHORS/aboutus/.mailmap. Welcome to SymPy!
fix test_import dir dependency
Merge pull request #2056 from bgee/import

Fix test_import directory dependency issue
Merge pull request #2054 from smichr/sum-prod-subs

fix Sum and Product _eval_subs
3785: rework multiplicity and handling in log
Merge pull request #2055 from smichr/3785

3785: fix multiplicity handling and log of Rationals
recognize b**(1/log(b)) and b**(1/(log(-b)+/-I*pi)) as E

The random test added will affirm this identity every time tests
are run. I already ran it several hundred times without error. The
code in power.py tries to fail quickly if it is likely that the
base and exponent don't match the target expression.