pcboot - int86 test: calling 16bit interrupts from protected mode

Implemented an int86 function, to call 16bit interrupts from protected mode. Testing with VBE (VESA BIOS Extensions) video mode switching and showing a highres high color test pattern. Accompanying article with more in-depth explanation: http://nuclear.mutantstargoat.com/articles/pcmetal/pcmetal04.html ... https://www.youtube.com/watch?v=U0UK1tnCZ60