s/uri/iri since we accept IRIs

implement a valid RFC3986 (URI) parser Up until now I used a "poor man" approach: the uri parser is barely a parser, it tries to extract the path from the request, with some minor checking, and that's all. This obviously is not RFC3986-compliant. The new RFC3986 (URI) parser should be fully compliant. It may accept some invalid URI, but shouldn't reject or mis-parse valid URI. (in particular, the rule for the path is way more relaxed in this parser than it is in the RFC text). A difference with RFC3986 is that we don't even try to parse the (optional) userinfo part of a URI: following the Gemini spec we treat it as an error. A further caveats is that %2F in the path part of the URI is indistinguishable from a literal '/': this is NOT conforming, but due to the scope and use of gmid, I don't see how treat a %2F sequence in the path (reject the URI?).

initial commit