Support for InverseFunctions and ChangesOfVariables

[oschulz]

With JuliaMath/ChangesOfVariables and JuliaMath/InverseFunctions we now have lightweight, low-bias packages designed to enable composability of packages that provide/implement or use variable transformation capabilities.

Would a PR that adds support for InverseFunctions.inverse and ChangesOfVariables.with_logabsdet_jacobian be welcome?

[oschulz]

Sorry, I completely lost track of this ... (for a very long time, ahem).

I'll put it back on my to-do list.

[oschulz]

Remind to self to get on this. :-)