Function parseRomanProgression

Parses a Roman numeral progression in a given key into an array of Chord objects.

• Case gives the third: I, IV, V major; ii, iii, vi minor
• What the numeral leaves unsaid comes from the key: vii in C major is Bdim, ii7 is Dm7, vii7 is Bm7b5. A third that is not the key's gives the plain chord of the case: II is D, iv7 in major Fm7
• Upper-case 7 is a dominant seventh (jazz convention): V7 G7, I7 C7, IV7 F7; the major seventh is written maj7 (Imaj7). dom is an alias (Idom7)
• Any other suffix is a chord type, read like parseChordSymbol (dictionary, then compositional); lower case adds the minor third: ii9 is Dm9, V7b9 G7b9, viiø7 Bm7b5, vii°7 Bdim7. An unknown suffix throws
• Accidentals move the key's own degree: bVII in C major is Bb, bII in A minor is Bb. In minor, VII and VI are the natural degrees (G and F in A minor), and vii°, vii°7, viiø7 stand on the raised leading tone (G#)
• Applied chords: V7/ii, vii°7/V, V/bVI (read in the major or minor key of the target, as its case says)
• Tritone substitution: subV7, subV7/ii
• Inversion figures at the end: 63 and 64 for triads (iv63 in A minor is Dm/F, I64 C/G), 65, 43 and 42 for the key's seventh chord (V65 G7/B, I65 Cmaj7/E, ii43 Dm7/A; viiø65, vii°43). A bare 6 stays the added-sixth chord (IV6 is F6)

Roots are named as the key writes them (bII in E major is F, V/vi in Db major is Ab). Example: parseRomanProgression("ii7 V7 subV7/ii Imaj7", "C major")