ocaml

Switch from iri library to uri master

We are agnostic as to the standard; I am switching because I think the uri library may be better maintained, or at least I have more confidence that I will be able to get what I need done due to the proximity of Anil Madhavapeddy to me at work. Regardless of the library we use for parsing, etc., we need to store our own *pure* representation in order for things like equality and comparison to work.