Allow using other NotNull annotations

[royteeuwen]

In our project we use the jetbrains annotations to specify NotNull. It would be convenient to either also support these, or to make a configuration available to specify the class name of what you want to use as NotNull annotations

[kbuntrock]

That is indeed a good idea. I'm currently in holidays for 3 weeks but I will add it as soon as I'm back.

[kbuntrock]

Back from holidays, will work on it asap. :) @royteeuwen

[josve]

Here is a suggested PR that adds support for this.

#111