v0.3.1

What's new

1. index property has been removed from document frontmatter. It is recommended that you now use navigation property in docgen.yaml to organize your navigation
2. Writing the navigation structure by hand is tedious. That is why this release introduces a new command: docgen nav that generates the navigation from your directory structure automatically.
3. Docgen will now automatically reload the site when you change docgen.yaml file.