Improve type annotation of Site.addEventListener

For specific event types certain event properties are always present.
Previously all event types...

Frontmatter support for JSON / TOML format

Add JSONC support for JSON Plugin

Added toml plugin

fix: error on comment-only YAML front matter

YAML front matters such as the following:

---
# Nothing here.
---

previously resul...

fix: Site.copy doing nothing for trailing slashes

Previously

site.copy("static/");

had no effect whatsoever because of the trailing slash.

...

New fs