Major Engine Revision

Hello!

The underlying engine was rewritten (after three long years) to occupy less memory and to be faster. Details of the changes are in `UPGRADE.md`.

You have made many awesome changes to the library (like `PROGMEM`, bicolor matrix support, etc.). 

If you are interested in using the updated engine, I can help you with parts of the merging process. Alternatively, you can apply the general changes to the root repository and maintain a bi-color support fork here.

If you need my help, I'll (finally!) be around to provide support.

Regards,
Gaurav