ADL 1.5 annotation formalisms

Some users want to be able annotate any node with a bit of formatted text (HTML, RTF, whatever). In the current ADL 1.5 specification, an annotation is just a name/value pair, so there would be nowhere to store the mime type of an annotation's value.

To allow the mime type to be specified, an annotation could become more like a DV_PARSEABLE. So, instead of this:

    ["design note"] = <"this is a design note on intelerance">

It would become this:

    ["design note"] = <
     formalism = <"text/html">
        value = <"this is a design note on intelerance">
    >

As with DV_PARSABLE, the formalism wouldn't be restricted to mime types:

    formalism : String 1 -- name of the formalism, e.g. "GLIF 1.0", "proforma" etc.