doc: Add filter images, fix typos.

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

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
core: Include GP_Fill.h in GP_Core.h.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
pywrap: core: Add GP_Fill

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