3562: Replace Method for MutableMatrix
Code quality improved
Support for map argument added
Test added for map. Code Now compliant with PEP8
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
MatrixExprs use real/integer/complex assumptions
move test_closed_group from sets to __init__
add Q.real/integer/complex_elements predicates
apart and cancel are nc-aware
2699: use xthreaded, not threaded in apart
806: Improve code style
modify xthreaded and xreplace to fail gracefully

- xreplace leave args that don't implement xreplace alone
- xtrheaded allows objects that don't rebuild to return unchanged
remove whitespace
MatrixElement Q.real/integer/complex
modifications to simplify

== add quick exit for simplify if expr is Atom

== 3712: try return factored expression more often

== 3730: use as_content_primitive and cancel
Merge pull request #1925 from smichr/3712

3712 - simplify changes
minor parser edits
matrix element types for Ident, Zero, DFT
Merge pull request #2032 from katjasophie/806_hyper.rewrite(Sum)

Issue 806: Implement hyper.rewrite(Sum)