Merge branch 'master' of github.com:tomchristie/mkdocs into docker-markdown-merge

Conflicts:
	docs/user-guide/configuration.md
	mkdocs/build.py
	mkdocs/config.py
	mkdocs/nav.py
	mkdocs/serve.py
	mkdocs/test.py
	mkdocs/themes/mkdocs/base.html