Improve Bitmaps sketch

[embedded-creations]

Requiring GIMP to load images and export to .c files is a little cumbersome. A better example would:

• Accept bitmaps directly from .h files or SD card, parsing BMP header directly, no tool modifications needed: https://github.com/jasoncoon/Teensy32x32MatrixSlideshow
• Show how to convert bitmap to .h file, using https://github.com/bitbank2/image_to_c or some of the tools mentioned in this thread: https://twitter.com/fast_code_r_us/status/1334348202833825792