type classes prototype

Hi all,
over the past few months we've been experimenting with an implementation 
of a type class feature along the lines of what Brian presented at last 
JVMLS [1]. This work is being added to the new "type-classes" branch as 
part of this PR:

https://github.com/openjdk/valhalla/pull/1886

While this is all still highly experimental, and a long way from being 
JEP-ready, we thought it might be worth sharing it here, as doing so 
will enable bleeding edge hackers (such as ourselves!) to carry out 
further experimentation, especially in the context of providing better 
support for new Valhalla-based numeric types [2].

More details on how the prototype works and which features it enables 
will be shared in due time, as we gather more experience with this 
feature. In other words, this is venue for experimentation, and NOT a 
proposal for inclusion in the Java platform, and any feedback should be 
providied while keeping that in mind.

Cheers
Maurizio

[1] - https://www.youtube.com/watch?v=Gz7Or9C0TpM
[2] - https://www.youtube.com/watch?v=xCdJb_zI5us