Trends API chord input

I made a more formal metasyntax for this a while ago.

About the “redundant” chords; Some of these chords used to have entries in the database, but I removed them manually from time to time to ensure that the database is clean and contains as few duplicate chords as possible, before the API receives an overhaul. Some chords are nonetheless different from others due to the possibility of embellishments (e.g. L3 is different from 3 because their add9 chords yield Em(add9) and Em(addb9) respectively).

Magic Chord sometimes gives S(3)3 instead of 5/6; this seems to be the proper way of addressing supermodal chords, but they are already rejected by the API and analyses containing any supermodal chord will not be found in the Trends page. Major V in Minor is the only supermodal chord accepted right now.

EDIT: It seems that all results of 4/4 are absorbed into b7 automatically, as does L2; this applies only to the root position, not 46/4 or 464/4 (or other inversions). If I remember correctly, this happens to all applied dominants and IV/IV, but the API document does not clearly indicate when such assimilation occurs.