[cairo] render text along path

[Dirk Schönberger]

> Apologies if this has come up before (as I suspect it has).  I need to be
able to render text along a path, in the style of the inkscape "Put on
> Path" function.

I don't think such functionality is (or should be) part of Cairo.
What I could see is some kind of utility method which works on cairo_path_t
which calculates the "normal vector" (or something like that) for a given
relative postition of the path.