TODO

- filtration of the double exts
- filtrations to modules and maps ...
- Hom, tensor products of torsion-free, projective, ... free modules are ...
- if a functor is reapplied to modules in a different context the output
  should be merged with the earlier output
- make the generation of the methods for multi-functors automatic
- GAPDoc & test examples
- ask Max:
  . why does GAP become slow when getting in the range
    of definig 1/2 million variables in Singular?
  . display issues ($COLUMNS) of external CAS
  . saving objects - Pickling using the IO package