Add support for continous mode

[martin.wickman@…]

libwiimote should have support for continuous mode as well. I'm thinking:

• Add a constant for wiimote_command()
• update_rpt_mode() in command.c to support 0x04
• process_btn in event.c: In continuous mode, buttons should be reported even though they have not changed

[dsmith]

added continuous mode flag and repeat button flag (r101)