Add markdown and base64 filters

Allow links to .md pages in pages contents

WIP shortcode

Use lazy front-matter regex

Using a greedy regex could lead to unintended consequences, like the
inability to syntax highlight a unified diff. This resolves issues like
that by using .*? instead of .* so that the closing +++ is matched as
soon as possible.

Prettier console output

Allow selecting a config file other than config.toml

0.0.1

Parse _index.md files as sections and render them