PEP8 fixes for euler_equations
Export euler_equations
Change output format to list, cleanup test_euler.py
Improve docstring of the euler_equation function
euler_equations: funcs/vars arguments support now arbitrary iterables
clear the cache once per file rather than after every test with pytest
Refactor setup_module methods out of sympy tests and use a single module level
fixture in conftest.py instead
Reformat some references
Add sphinx documentation for old assumptions in the core
Ensure SYMPY_DEBUG env variable contains only True or False

Evaluating it unchecked is an unlikely yet possible vector of attack,
e.g. one can gain root privileges if there's a script importing sympy
with setuid bit on it.
8046;16.1-3: enhance and correct Add._eval_is_(positive|negative)

The checks for a.is_zero were removed because those are already
handled outside of the loop.
8046;17: Add._eval_is_imaginary modifications
Merge pull request #7936 from skirpichev/old-assump-docs

Add sphinx documentation for old assumptions in the core
Merge pull request #8142 from skirpichev/euler2

Improvements for euler_equations
Merge pull request #8146 from immerrr/strict-eval-of-sympy-debug

Don't evaluate arbitrary text coming from SYMPY_DEBUG variable
Merge pull request #8162 from smichr/8046

Add._eval_is_(pos, neg, imag) changes
correct issue numbers
Merge pull request #8151 from pbrady/pytest_clear_cache

clear the cache at the start of file [pytest]
Merge pull request #8152 from pbrady/refactor_disabled

Refactor setup_module methods [pytest]
unbounded -> infinite