absolute(
base_url,relative_url) ->resolved
Resolve a relative URL against a base URL per RFC 2396 section 5.2
If relative_url has a scheme, it is returned as-is (already absolute).
Otherwise, missing components are inherited from base_url following
the RFC priority: scheme, then authority, then path (merged via
dot-component normalization), then params, then query. Fragment is
always from the relative URL. base_url may also be a parsed table.