Major improvements

• The standard column 'onset' has been renamed to 'mc_onset' and 'mn_onset' has been added as an additional standard column.
• Parse TSV files as Annotations objects
• Parse.attach_labels() for inserting annotations into MuseScore files
• Prepare detached labels so that they can actually be attached
• Install "ms3 extract" command to the system
• Including da capo, dal segno, fine, and coda for calculating 'next' column in measures tables (for correct unfolding of repeats)
• Simulate parsing and table extraction
• Passing labels_cfg to Score/Parse to control the format of annotation lists
• Easy access to individual parsed files through Parse[ID] or Parse[ix]
• parse annotation files with diverging column names