Converting SQLite database to feather

[edublancas]

Hey guys, just created a script to convert the track_metadata.db file to feather, it contains the same information than the .txt files + some other information. Using the txt files may cause trouble since the unique_tracks file does not have the artist_id (and when I joined by artist_name I noticed there are some duplicates) - I updated the readme

# export track metadata
./process/clean/export_track_metadata data/raw/AdditionalFiles/track_metadata.db data/transform/mxm_dataset_50.feather data/transform/track_metadata.feather