add `_grid.binary`

[andr-ew]

adds a behavior property that controls which input / output routines to use. value persists between momentary -> toggle but clears when behavior changes to trigger or momentary. a level_trigger property is added for trigger's level.

[andr-ew]

current binary may be renamed to held or bin or the like

[andr-ew]

erp actually it might be better to let user land handle clearing out value, that keeps the nest end tidy - ~~just need to add #100 for momentary & toggle~~ -> use clear()