add support for custom HTTP handlers / interceptors

Hi

i have implemented the solution for custom HTTP handlers as described [here](https://github.com/atomify/atomify/issues/41). Could you please have a look at this and - if ok - integrate this into master? For the project i am currently working on this feature is really important as we have to serve some static content differently than atomify does by default (mainly for back end webservice proxying).

Thanks, Andi
Why not just a noop? `… || Function()`