Started serre quotient categories.
Merge remote-tracking branch 'Sepp/master'

* Sepp/master:
  ToDoList for GeneralizedMorphismObject
  Example composition of generalized morphisms
  Added missing CanComputes in GeneralizedMorphismCategory.gi
Added a readme.
VectorSpacesForGAPDays
Fixed a bug.

Found it because I copied the method to the slides.
So the talk was indeed useful.
Documentation

Documentation of Add-Methods in UniversalObjects.gd
- Kernel
- Cokernel
- Initial Object
- Terminal Object
- Coproduct