Added AddFrame() and YUV422 support

This release is in response to testing the M5Stack CoreS3 device. It has a 640x480 color camera (GC0308), but it's a low cost device that only outputs uncompressed frames. In order to generate JPEG compressed images, it needs to use a software encoder. I added the YUV422 input type to allow a faster path to compress images from this and other cameras.

Initial Release

This is code that I optimized many years ago for low-end PCs, but finds new life on modern microcontrollers. A simple API, yet covers most things that people need to accomplish with JPEG encoding. Requires 3-4K of RAM and should run well on any 32 or 64-bit CPU.