* [bitmap] on move, clear old OPAQUE cells #1527
* update ncvisual_blitter_geom() documentation #1547
* replace some ncvisual_blitter_geom with NCVISUAL_OPTION_VERALIGNED
* [normal] replace ncvisual_blitter_geom with NCVISUAL_OPTION_VERALIGNED
* [intro] use ncvisual_blitter_geom() correctly #1547
* ncvisual_blitter_geom: only set *blitter on success