Add multibind class provider

[Letsch22]

Adds the MultiBindClassProvider which provides instances of classes from a list of class types when using the multibind API.

Resolves #45

[jstasiak]

Thank you for this, I'll have to think about this interface

[KrzysztofMadejski]

I just ran into the same need. It's quite of a gap that multibind can't work with ClassProvider as normal bind would.