Convert GObject Introspection metadata into IIGlue JSON format.

This simple XSLT script expects the GObject Introspection metadata to
already have been extracted from the source code as a GIR XML
document.  The output is in JSON format, structured in the same way as
IIGlue analysis output.  It's definitely not *complete* IIGlue
analysis output; we only convert the small subset of IIGlue
annotations that our own IIGlueReader class expects to find.

The intent of this script is to let us pretend to have run IIGlue on
libraries that other people have already hand-annotated.  Rather than
actually running IIGlue, we extract IIGlue-like information from the
annotations already present.