RGBDK experimental library

SDCC 4.0.3 #11777 and higher now supports mappings for RGBDS assembler.

This is an attempt to make some kind of library, that allows to use advantages of both RGBDS assembler and SDCC C compiler.

You need SDCC 4.0.3 #11777 or higher for here: http://sdcc.sourceforge.net/snap.php

You need RGBDS 0.4.1 or higher from here: https://github.com/rednex/rgbds/releases

Based on gb-starter-kit by ISSOtm: https://github.com/ISSOtm/gb-starter-kit

I appriciate your help and feedback.

Tony.