Implement Abs._eval_is_even/odd helpers

fixes #8631
Revert 893daf4 and add test for issue 8642

fixes #8642
Merge pull request #8638 from skirpichev/8631-fix

Implement Abs._eval_is_even/odd helpers
Fix TrigonometricFunction._eval_is_rational for rational args

closes #8653
Fix exp/log._eval_is_rational for rational args
Merge pull request #8644 from skirpichev/8642-fix

Revert 893daf4 and add test for issue 8642
Use bold instead of a code tag in the GitHub release Markdown
Sign Error in Unrad Function issue #8622

Added Test for SIgn Error in unrad

	assert unrad((root(x + 1, 5) - root(x, 3))) == (x**5 - x**3 - 3*x**2 - 3*x - 1, [], [])

Added Test for SIgn Error in unrad issue #8622

Added Test for issue #8622
assert unrad((root(x + 1, 5) - root(x, 3))) == (x**5 - x**3 - 3*x**2 - 3*x - 1, [], [])
Merge pull request #8654 from skirpichev/8653-fix

Fix TrigonometricFunction._eval_is_rational for rational args
Merge pull request #8667 from asmeurer/release-github

Use bold instead of a code tag in the GitHub release Markdown
Fix Pow._eval_is_integer in case base.is_integer is False

closes #8641
fixing power for nonnegative integers
Merge pull request #8661 from kaushik94/nonnegative-power

fixing power for nonnegative integers
Changed solve to work for non-linear piecewise functions

Changed solve to fix #8587 and added a test.
Merge pull request #8645 from skirpichev/8641-fix

Fix Pow._eval_is_integer in case base.is_integer is False
Merge pull request #8680 from nishithshah2211/issue8587

Bug fix #8587
Merge pull request #8647 from aktech/master

Fix sign Error in Unrad Function issue #8622 …
Add AMiT Kumar to AUTHORS/aboutus. Welcome to SymPy!
Parial fix for issue #8677: exclude early exit in equals() for Mod
Add Nishith Shah to AUTHORS/aboutus. Welcome to SymPy!