frontends: added libcaca video implementation.
chip8: added CPU file.
main: added audio frontend support.
frontends: added SDL audio implementation.
chip8: audio is now supported.
main: added linked list helper functions.
main: modified machine structure to use generic lists instead of custom ones.
main: removed short option handling from command line parsing functions.
main: added input frontend support.
frontends: added basic SDL input implementation supporting quit events.
frontends: added basic libcaca input implementation supporting quit events.
main: added support for quit events in machine main loop.
main: added support for keyboard input.
frontends: SDL input now reports key events.
frontends: libcaca input now reports key events.
chip8: input is now supported (using default set of keys from 'a' to 'p').
main: added random seed initialization.
chip8: machine selection is now configurable.
main: all controllers and CPUs are now selectable in menuconfig.
main: help now automatically displays supported machines and frontends.