Changelog for gb-synth-0.2.0.2

Changelog

Fix Envelope module documentation (decay/release described as "exponential" but implementation is linear).
Add gb-vector as ecosystem companion in README.

Fix Haddock cross-references in Effects and Pattern modules.
Fix README chord progression descriptions and missing Pattern import.
Remove -O2 from library and test ghc-options (consumers set their own optimization).

GBSynth.SFX: 13 ready-to-use sound effect presets (laser, explosion, impact, alert, click, powerup, coin, jump, heal, defeat) plus pre-rendered drum samples (kickSample, snareSample, hihatSample). All built from synthesis primitives, no sample files.
GBSynth.Chord: Programmatic chord construction. Quality type (Major, Minor, Diminished, Augmented, Sus2, Sus4), chord / inversion / chordProgression builders, and built-in progressions (pop1564, blues145, minorClassic).
GBSynth.Effects: Post-processing effects — bitCrush, echo, fadeIn, fadeOut, reverseSignal, mix.

Eliminate partial functions: tail → drop 1 in Oscillator and Synthesis, maximum / foldl1 → safe foldl' with empty list guards in Render.

Initial release.

Oscillators: sine, square, saw, triangle, noise, pulse with configurable duty cycle
ADSR envelope generator with attack, decay, sustain, release stages
Instrument definition with oscillator type, envelope, and harmonics
Multi-channel pattern sequencer with note events and rests
Song structure: sections, tempo, time signature, instrument assignment