ENH: Add first pass at a registries

[Kai-Striega]

This PR includes the first pass at a speaker and talk registries. It manages each as a .toml file which contains the required data about the speaker or talk respectively. Further it includes checks that the .toml files are correctly formatted, which can also be run in CI.

[Kai-Striega]

This is terrible English 😓 you can see I wrote it very late last night

[elena]

Wondering if we should be formalising syntax or maybe even aligning the "front matter" to align with the way they use it in ssgs eg:

• https://gohugo.io/content-management/front-matter/#front-matter-formats
• https://jekyllrb.com/docs/front-matter/
• https://www.getzola.org/documentation/content/page/#front-matter

If we matched the syntax and semantics we could just cheaply plug in to one of these without a translation layer.

[elena]

Like a perfectly normal person I started a comparison table:

Jekyll	Zola	Hugo
page.content	title = ""	aliases (string array)
page.title	description = ""	build (map)
page.excerpt	date =	cascade (map)
page.url	updated =	date (string)
page.date	weight = 0	description (string)
page.id	draft = false	draft (bool)
page.categories	render = false	expiryDate (string)
page.collection	slug = ""	headless (bool)
page.tags	path = ""	isCJKLanguage (bool)
page.dir	aliases = []	keywords (string array)
page.name	authors = []	lastmod (string)
page.path	in_search_index = true	layout (string)
page.slug	template = "page.html"	linkTitle (string)
page.ext	[taxonomies]	markup (string)
page.next	[extra]	menus (string, string array, or map)
page.previous		outputs (string array)
		params (map)
		publishDate (string)
		resources (map array)
		sitemap (map)
		sites (map)
		slug (string)
		summary (string)
		title (string)
		translationKey (string)
		type (string)
		url (string)
		weight (int)