Roles' HOWs deserve better documentation

[Kaiepi]

The problem

Roles are complex. This is not a bad thing per se, but they need good documentation in order for people to completely understand how they work. While the objects page does a good job of explaining them in the kind of terms people tend to work with them with, the documentation on their HOWs is lacking.

Suggestions

Expand the documentation on Metamodel::ParametricRoleGroupHOW, Metamodel::ParametricRoleHOW, Metamodel::CurriedRoleHOW, and Metamodel::ConcreteRoleHOW.

This is something I'm willing to work on.

[JJ]

Please do that by all means. But make sure to eliminate the note saying "Don't use this at home, kids" of the ones that are already documented. And thanks!