gp_codegen: Add idx to channel.

The channel.idx describes position of the channel in pixel (from left).

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
doc: Finish logo and favicon.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
doc: Cleanup loaders docs a bit.

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

Point filters are now implemented using ApplyTable generic filter.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
loaders: PNM: Fix aligment issues in save_ascii_rgb888

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