Handle unicode literals properly in matrices

Fixes #7604
Added a few rules for imageset simplification
Implement __ne__() by calling __eq__()

The __ne__() operator should return "not __eq__()". Alternatively, one can copy
& paste the algorithm from __eq__() and negate the answer right before each
return. But anything else means there is a potential bug.
Update piecewise.py

Corrected a typo.
Merge pull request #7647 from coder006/typo

Correct a typo in piecewise.py
Merge pull request #7645 from certik/ne

Implement __ne__() by calling __eq__()
Added Ambar Mehrotra to the AUTHORS/aboutus. Welcome to SymPy
Merge pull request #7625 from hargup/imageset_simplification

Added a few rules for imageset simplification
Incomplete doc in deutils

A line is complete in docs in _desolve in deutils. It can be more than one thing possible there. I need suggestions to complete this sentence.
Merge pull request #7613 from clsn/str_unicode

Handle unicode literals properly in matrices
Add Mark Shoulson to the AUTHORS/aboutus. Welcome to SymPy
Completed the doc sentence of _desolve in deutils.py

The sentence, This is useful when the function, was incomplete earlier. It is now replaced with `This is useful when the expression has more than one function in it.`
Merge pull request #7657 from KDMOE/typo_deutils_desolve

Incomplete doc in deutils [skip ci]
Add some names to .mailmap
polished code and tests
Merge branch 'master' of https://github.com/sympy/sympy into basicvector