1.15.0 - better `parametrize_plus` and smaller dependencies

• Better support for pytest.param in parametrize_plus and also in fixture_union and fixture_param[s]. Improved corresponding ids. Fixed #79 and #86

• New @ignore_unused decorator to protect a fixture function from the "NOT_USED" case happening when the fixture is used in a fixture union.

• Removed six, wrapt and enum34 dependencies

• (Internal) submodules reorganization for readability

• (Internal) suppressed a lot of code quality warnings

See documentation page for details.