Liara

* Fix a packaging issue.

* Improve document handling: Documents without a trailing newline are now supported, previously they would cause an error.
* Improve configuration: Empty configuration files are now supported.
* Fix `list-files` requiring a type to be specified.
* Add `liara.query.Query.exclude`.
* Override `base_url` when serving locally. This was previously documented to work, but not implemented. As part of this change, `liara.site.Site.set_metadata_item` was added.

liara 2.0 is a complete rewrite of liara, with no shared code with the 1.x series. liara 2 is now template & content driven, and no longer just a library which simplifies static page generation. Unlike the 1.x series, it is possible to use liara 2 without writing any Python code.