create a standard for external tools to store data in tox.ini

Issue #225 on hold
Ronny Pfannschmidt
created an issue

since https://bitbucket.org/pytest-dev/pytest/issue/567/use-of-pytest-in-setupcfg-collides-with

i think its there is need for a standard ruling on how to put other things into tox.ini that will be collision-free in future

i propose prefixing of sections of tools with external or tool

so [pytest] would become [tool:pytest]

same would go for pep8/pyflakes/...

we might also want to get an idea on wah pypa wants there