fix tox to test examples again
add detox tox env for faster testing
clean up makefile, add tox target
add extra group for installing dev requirements
clean up contributing doc, build with docs
expand issue template
add pull request template
On issue #1773, we wanted use issue templates to accomplish two things:
1. guide questions into StackOverflow and IRC channel
2. not duplicate CONTRIBUTING content
To resolve these, ISSUE_TEMPLATE is added to remind users not
to ask questions.
