Provide ostream based API

[ktf]

I would like to use FairLogger with some external component, which has the possibility to pipe log messages on a provided std::ostream. Is there any way we could have a wrapper around Logger which is std::ostream derived, while still using FairLogger as backend?

[rbx]

I have no found an easy way of doing this so far. Certainly I would like to avoid inheriting from ostream directly, as it can be quite complex.

But a wrapper as you suggest might work. Do you have a possible solution for this in mind?