more implementation notes
blind: change button action when blind was just lowered completely

after blind was lowered completely, next short button press should
open it completely.  previously it chose the middle position.
suart: fix input capture interrupt handling bug

alex cornejo points out that when using interrupt capture, the enable
bit is never turned off, which will prevent ever capturing a full
byte.  i introduced this bug recently -- it's not present in
previous versions of the suart code (e.g., in my irmetermon project).