Add example for grayscale displays

examples/uc8151d_grayscale_test.py

@@ -0,0 +1,56 @@
+import time
+import board
+import displayio
+import busio
+import adafruit_uc8151d
+
+displayio.release_displays()
+
+clk = board.GP10
+si = board.GP11
+dc = board.GP8
+cs = board.GP9
+rst = board.GP12
+busy = board.GP13
+
+display_bus = displayio.FourWire(
+    busio.SPI(clk, si), command=dc, chip_select=cs, reset=rst, baudrate=1000000
+)
+
+time.sleep(1)
+
+display = adafruit_uc8151d.UC8151D(
+    display_bus, width=152, height=152, busy_pin=busy, rotation=180, grayscale=True
+)
+
+
+bitmap = displayio.Bitmap(152, 152, 4)
+
+# Draw Black
+for x in range(0,152):
+    for y in range(0,38):
+        bitmap[x, y] = 0
+#Draw Dark Gray
+for x in range(0,152):
+    for y in range(38,76):
+        bitmap[x, y] = 1
+#Draw Light Gray
+for x in range(0,152):
+    for y in range(76,114):
+        bitmap[x, y] = 2
+#Draw White
+for x in range(0,152):
+    for y in range(114,152):
+        bitmap[x, y] = 3
+
+palette = displayio.Palette(4)
+palette[0] = 0x000000 # Black
+palette[1] = 0x404040 # Dark Gray
+palette[2] = 0x808080 # Light Gray
+palette[3] = 0xFFFFFF # White
+
+g = displayio.Group()
+t = displayio.TileGrid(bitmap, pixel_shader=palette)
+g.append(t)
+display.show(g)
+display.refresh()