Generator.get_files backwards compatibility for 1 path

This should prevent outdated plugins with generators from failing.
Also fixes #1382.
Fix "server didn't start" error message in develop_server.sh

It has port 8000 hardcoded into it, which is confusing when the server runs on
another port.
Enhance feedback and contributing guidelines

Many folks ask for help (via IRC or filing GitHub issues) without
sufficient detail and/or without first determining if the answers to
their questions might be better sourced elsewhere. These
documentation changes encourage users to follow certain guidelines
when reaching out for help.
Add troubleshooting info to CONTRIBUTING docs
Change IRC webchat provider to Kiwi IRC
Promote URL settings docs to top-level heading
Update changelog in preparation for release
Build binary wheels when publishing to PyPI
Additions to changelog
Fix SLUGIFY_SOURCE docs
setup.py version should inherit from __init.py__
Bump version 3.4.0
Work around setup.py encoding issue in last commit
Revert setup.py changes. Ensure universal wheels.

Attempts at fancy version number handling in setup.py caused more
problems than they were worth, including Travis CI build failures.

The setup.cfg key for universal binary wheel generation apparently
changed at some point, so that was updated as well.
Increment development version to 3.5.dev
Merge pull request #1387 from eliben/fix-devserver-port

Fix "server didn't start" error message in develop_server.sh