Add an SDL sound backend and use it instead of spawning an external

[micropolis] / images / spacer.xpm

/* XPM */
static char *noname[] = {
/* width height ncolors chars_per_pixel */
"126 2 2 1",
/* colors */
"+ c #3f3f3f",
"# c #bfbfbf",
/* pixels */
"+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++#",
"+#############################################################################################################################",
};