v0.8.0 — style packs

Listen: https://catdogbark.github.io/bitComposer/ — two seeds in all three palettes, regenerated for this release (half of the snes songs draw a pack).

Style packs: an instrument set paired with the arrangement habits of the scores it imitates. Four packs, each reviewed by ear against plain snes on comparison pages, plus the engine pieces they needed and the fixes the reviews turned up.

• Style pack megamanx (Mega Man X), designed from the game's own SPC sample bank: a driven, chorused lead guitar, a chugging rhythm guitar, a dry pulse synth, synth brass, a string pad, a soft lead, a snapping synth bass and a tight kit, all synthesised to the measured shapes; habits: fast tempos, intense energy, minor keys, stab and rhythmic harmony on power chords (new habit power_chords: root, fifth, octave), a new riff bass style (a one-bar root / octave / fifth riff), busy drums, no swing, broken-octave and gallop arps, a pulse-synth counter-line half the time, and the game's echo: a new slap delay (48 ms, written as a tick delay under a row) with bounce stereo.
• Style pack evermore (Secret of Evermore): warm and dark ensemble pads, a drone, a breathy flute, an "oo" choir, tubular bells, frame drum, brushed snare and a soft click; habits: slow tempos, chill energy, minor keys, linear forms, sustained harmony, a new drone bass style (one held note per chord, sliding between roots), sparse drums with a 40% chance of no kit at all (new pack habit drumless), wet centred echo on a quarter or dotted-eighth delay (packs can now weight echo_delay and the song form).
• Style pack mana (Secret of Mana): celesta, kalimba, steel drum, wind chimes, whistle, pan flute, a glassy chorused pad, and a hand-percussion kit (conga on the tom slot, shaker as the hat, tambourine as the open hat, woodblock as the rim); habits: major and pentatonic keys, pulse / rhythmic / stab harmony, octave and walking bass, light swing, bouncy arp figures (packs can now weight arp.FIGURES), kick and snare trimmed back.
• Arp echo: only the arp's accented steps are sent, and the arp send tapers with tempo (full to 130 BPM, gone by 170), so a fast pizzicato arp no longer turns into a stream of ticks between the plucks.
• Echo stereo: the "spread" mode (every repeat hard on the far side of its part) is replaced by "centre" (repeats under their source). A copy arriving a quarter second late from another direction was heard as a second player coming in late rather than as a room.
• Style packs (--pack, bitcomposer/packs.py): an instrument set paired with the arrangement habits of the scores it imitates. First pack ffvi: string section with ensemble beating (a long loop carrying sharp and flat copies that beat at 1.6 Hz), horn, trumpet, oboe, clarinet, piano, music box, pipe organ, bowed basses, and an orchestral kit (timpani on the tom slot, bass drum, orchestral snare, suspended cymbal); habits: ostinato (3+3+2) and pulse harmony modes, a horn counter-line in 60% of chorus and bridge patterns, timpani rolls into choruses, slower tempos, no swing, hats trimmed, a wetter and wider echo. Half of snes songs draw a pack when --pack random; the song message names it. Widget: PACK picker in the COMPOSE tab.