make the demo site generate no invalid links
show help if nikola check is called without options
generate empty tag page when there are no tags (make check happy)
permalink without '.'
Merge pull request #339 from zikzakmedia/master

permalink without '.'
semi-fix for #329
re-enable find-sources in nikola check
make sitemap report target for check command
Use different basename for gallery tasks that delete excluded files (Fix #340)
RSS default header template. Rename lang to language
Monkeypatch Doit's command help (Fix #151)
Merge pull request #341 from zikzakmedia/master

RSS default header template. Rename lang to language
updated changelog
flake8
execute execute
fix tests
Bad usage of mutable as default
flake8
flake8
separate parsing from reading file contents, for easier testing