Gset preparation without the use of amt-tools library

[anthonio9]

amt-tools library is a dependency coming from the world of FRETNET, however getting rid of it would greatly increase the my understanding of the code and decrease the dependency list.

amt-tools is only responsible for reading the pitch labels from the GuitarSet dataset, then filling the blanks with zeros. That's about it. The not very comfortable feature of the GuitarSet is how it uses jams to store the data, think about it!

[anthonio9]

amt-tools library is now only used in tests as a reference. It seems that the new approach works fine. When working on this issue I've found out that the warning

/home/antoni/Documents/Aalto/ThesisWork/Source/EvaluationOfResearchPapers/penn/penn/data/preprocess/core.py:274: RuntimeWarning: divide by zero encountered in log2
  pitch = 2. ** np.interp(new_times, times, np.log2(pitch))

comes from the fact that some strings are completely empty and are filled with 0s, should that be fixed somehow?