Include files and data structures

This project uses the following include files:

Nothing interesting here, just a function prototype.
This contains the GIF compressor's work area data structure, gif_context_t. The work area is used for compressing the bitmap to GIF format. Since the topic of GIF compression is beyond the scope of this book I won't go details. All of the global variables that were present in the original GIF encoder were gathered up and placed into a data structure.