I added Full ADSR and Velocity support

I added sliders for Attack, Decay, Sustain, and Release, all of which affect the output sound. I also programmed velocity support, so how hard a key is pressed affects a note’s volume. I also added square waves (with duty cycle control), triangle waves, and sawtooth waves. The hardest one for me was triangle waves, which I originally had a janky setup that made half-triangle waves oscillating between -1 and 0, but eventually landed on osc = 1 - 4 * abs(mem[phase_address + i] - 0.5); after doing some research online.