sequence: Add a function to play the previous animation

[arturo182]

If we treat a Sequence as a list of animations that we switch between manually, then having a previous function to counteract next would be great :)

[dhalbert]

This is OK by me!

[FoamyGuy]

Looks good to me. Tested successfully on a NeoTrellisM4 with 8.0.3 beta with this modified example:

import adafruit_trellism4
import time
from adafruit_led_animation.animation.solid import Solid
from adafruit_led_animation.sequence import AnimationSequence
from adafruit_led_animation.color import RED, BLUE, YELLOW, GREEN, PINK


trellis = adafruit_trellism4.TrellisM4Express(rotation=90)
trellis.pixels.brightness = 0.2

solid_blue = Solid(trellis.pixels, color=BLUE)
solid_red = Solid(trellis.pixels, color=RED)
solid_yellow = Solid(trellis.pixels, color=YELLOW)
solid_green = Solid(trellis.pixels, color=GREEN)
solid_pink = Solid(trellis.pixels, color=PINK)

animation_sequence = AnimationSequence(solid_blue, solid_red, solid_pink, solid_yellow, solid_green, auto_clear=True)

while True:
    animation_sequence.animate()

    pressed = set(trellis.pressed_keys)
    for key in pressed:
        print(key)

    # Pressing the button pauses the animation permanently
    if pressed:
        animation_sequence.previous()
        time.sleep(0.3)