doc: Autogenerate table of all examples + cleanup.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
doc: Remove unused pixel_types.txt.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
doc: Add C core documentation page + cleanup.

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