Parallelizing excerpt creation [FEATURE]

[johentsch]

Is your feature request related to a problem? Please describe.
Creating, say, all 2-measure excerpts takes a long time.

Describe the solution you'd like
The excerpt creation tasks should be parallelized.

Avenue

• Follow the mechanism used in corpus.py
  • Write a function that takes an MSCX object and the same parameters as MSCX.store_excerpt().
  • Compile a list of tuples where each tuple corresponds to the positional arguments for one call to the function (no keyword arguments possible)
  • Use starmap.