Test 6502 assembler programs. Generate binaries with:

xa -w -Istdlib/ sample_programs/test.s

xa is a cross-assembler and utility suite for 65xx series processors. It's
included in many package repositories as `xa65', including Homebrew on OSX in
the Debian repositories. The source is available at
http://www.floodgap.com/retrotech/xa/

Sample programs:

        alphabet.s      Prints A through Z to the terminal. Demonstrates basic
                        terminal output.
        colors.s        Prints a bunch of A's in different colors using vterm
                        mode. Demonstrates paints and vterm output.
        echo.s          Echos everything read from stdin to stdout, transforming
                        letters into uppercase. Demonstrates terminal input.
        minigame.s      Move a character around a vterm with hjkl. Demonstrates
                        a more complex vterm application.
        spam.s          Writes A through Z repeatedly, filling the vterm.
                        Demonstrates vterm output and how to do indirect
                        addressing to address the whole vterm.
        stdlib_test.s   Demo program displaying the functionality of the
                        standard library.
