RSS and Atom feed parser, using expat via the luaExpat binding. 
Similar to the Universal Feed Parser (https://feedparser.org), 
but less good.
feedparser requires LuaExpat, so you might want to make sure 
you've got that installed.
this feedparser is directly inspired by the Universal Feed Parser
by Mark Pilgrim. the output for a parsed feed is similar enough that 
you may consult his site for reference 
( https://feedparser.org/docs/reference.html )
Usage:
local feedparser=require("feedparser")
-- note that for Lua < 5.3, the require exports a global "feedparser"
-- In 5.3 and later, it does not.
local parsed = feedparser.parse(xml_string, optional_base_url)
--parsed will be a table of elements containing more or less:
{
	version=format name and version ("atom10" or "rss20" etc),
	format="atom" or "rss",
	feed={ --feed information
		title="Feed Title",
		subtitle="Or: How To Write Haphazard Documentation In 12 Easy Steps"
		rights="rights, if any.", --taken from the "rights" or "copyright" tag.
		generator="Particularly Clicky Keyboard", --generator, if present. Atom feeds provide this tag, as does rss, under admin:generatorAgent
		
		author="John Doe",
		author_detail={
			name="John Doe",
			email="",
		},
		link="https://example.org/",
		links={
			1={
				rel="alternate" or "self" or "related" or "via" or "enclosure" or "something else i forgot to mention",
				type="content type of the page the feed points to, if present",
				href="https://example.org/", --url is resolved.
				title="link title, if any"
			},
		},
		updated_parsed=1071340202, --parsed date string
		updated="2003-12-13T18:30:02Z", --raw date string
		
		id="urn:uuid:uuid-if-present-nil-otherwise",
		contributors={
			--contains a list of contributors, if present. Otherwise, an empty table.
		},
	},
	entries={
		1={
			enclosures={	},
			id="urn:uuid:1225c695-cfb8-4ebb-whatever-if-present",
			link="https://example.org/2003/12/13/atom03",
			links={
				1={
					href="https://example.org/2003/12/13/atom03",
				},
			},
			updated="2003-12-13T18:30:02Z",
			updated_parsed=1071340202,
			title="The Exciting conclusion of Atom-Powered Robots Run Amok",
			summary="Some text.",
			"contributors"={
				--if any. othersie, empty table.
			},
		},
		...
	},
}
The following will NOT appear in the parsed feed table:
feed.info
feed.info_detail
feed.title_detail
feed.subtitle_detail
feed.rights_detail
feed.textinput
feed.cloud
feed.publisher
feed.publisher_detail
feed.tags
feed.ttl
feed.licence
feed.errorreportsto
entries[i].title_detail
entries[i].publisher
entries[i].source
entries[i].comments
entries[i].licence
namespaces
encoding 		--this is pretty important, so will be implemented sooner than anything else, if anyone asks for it.
status
gref
etag
modified
headers
bozo
bozo_exception