Feature request: Support for taxonomies

[theowenyoung]

It would be great if Zine could support taxonomies, similar to Zola’s implementation.

Taxonomies allow grouping content by categories, tags, authors, years, etc., and automatically generate listing pages like /tags/ and /tags/rust/.

Example in Zola:

taxonomies = [
{ name = "topics", feed = true },
{ name = "categories", feed = true },
]

and in content:

[taxonomies]
tags = ["rust", "static-site"]
categories = ["development"]

This feature would make Zine much easier to use for blogs and knowledge-base style sites.