pytest-capture log seems to have been abandoned in favor
of pytest-catchlog
pytest-catchlog is no longer maintained; pytest-3.0 will emit
warnings about deprecated features, and pytest-catchlog
makes use of the deprecated "pytest_funcarg__" way
to declare fixtures
Re-using the built-in tmpdir fixture fixes pytest-dev/pytest#1083
Also with latest pytest there's no need to use --assert=plain on py35 anymore
Fixes#3699Fixespytest-dev/pytest#1083
Then folks who don't use tox can do `pip install -r
dev-requirements.txt`
Since this is pip, which created the idea of requirements files, it
seems nice for the project to have one to showcase the idea.
Also cleaned up the tox.ini and made it more compact (fits now on my
laptop screen) and consistent.
