exponential running time/ memory consumption. This problem only affected a
fraction of PDB entries.

That's certainly better than segfaulting

cleaned up file list parsing for module and pymod macros

- When None values are observed, ROC and Enrichment were computed
  inconsistently since the order in which the values occured played a
  role. Now, None values are ignored.
- Enrichment was computed inconsistently, when the same value occured
  multiple times. Now, the average enrichment is taken, similar as in
  ROC calculation.

when adding a new column

in case of an empty table (what we actually want...)

can be outsourced in the corresponding insert chain function

relative paths