Thin El wrappers over seed primitives that form the public HTTP API for
El programs. Covers GET/POST/DELETE, header-map variants, binary streaming
to file, form-auth, v1/v2 server dispatch, and http_response envelope
construction. Documents two new seed primitives needed: __http_do_map and
__http_do_map_to_file (ElMap-accepting variants to avoid needing map
iteration in El).
Will Anderson