Removed redundant part of code in compilef.
Replace free_symbols over atoms
merge conflict resolution
remove str from a test file added
Merge branch 'master' into clear-atoms(Symbol)
merging master with newly updated files
modify ode as to eliminate redundant lines
remove _find_first_symbol as no use
changing constructor as to support Integral and Sum forms
reverted back the constructor.py by removing simplification codes
Catch ZeroDivisionError in is_constant
Add test for issue 4503, closes #4503
Move sets.py to sympy.sets (from the core)
Remove deprecated tsolve function, fix #6484
Remove deprecated zeros([r, c]) and ones([r, c]) syntax, fix #6480
Remove deprecated Integral.transform() inverse option, fix #6479
Remove deprecated option 'simplified' from methods of MatrixBase class, fix #6481
Remove deprecated matrix_add/multiply functions
Remove deprecated DenseMatrix.row(i, f) and .col(i, f) syntax
Remove deprecated Basic.compare_pretty method, fix #4590