[HarfBuzz] Template or sample code for writing a shaper for harfbuzz-ng?

[Chapman, Christopher]

Tom asked:

>Isn't the Arabic shaper a good enough example for new shapers? (I
>honestly don't know, I'm just asking).

It is a start, but as Ed also asked:

>Also are there any guidelines on general "do's" and "don't"s when
>writing shaping extensions for harfbuzz-ng in order to maximize
>efficiency and avoid pitfalls?

I also would like to contribute, and I also would like a little more guidance on how best to do so.  :-)

While I'm asking questions along those lines, let me also ask this:

Who's writing shapers right now?  Which ones?

I'd be happy to contribute by assisting folks with ongoing work and/or writing a new one (Behdad had suggested Khmer as a possibility for the latter). 

Cheers,
Christopher