doc: Add two more examples.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
doc: text: Fix API docs.

* The GP_Text() function prototype wasn't updated
  when background color was added to the parameters.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
demos: c_simple: Remove abort.c

Signed-off-by: Cyril Hrubis <metan@ucw.cz>