Add a define in both the source and Makefile for enabling logging of z80 instruction address/cycle counts. Fix Z80 in/out instructions to eliminate assumptions about which registers are stored in native regs. Fix read_16 to not corrupt the low byte when the read has to call into a C function.

#version 110

uniform sampler2D textures[2];

varying vec2 texcoord;

void main()
{
	gl_FragColor = mix(
		texture2D(textures[0], texcoord),
		texture2D(textures[1], vec2(texcoord.x, texcoord.y - 1.0/512.0)),
		sin((texcoord.y * 512.0 - 0.75) * 3.14159265359) / 2.0 + 0.5
	);
}