update-option will make the range-descs and line-descs option up to
date with the latest buffer modfications, changing the ranges/lines
to where they moved according the modifications since the timestamp
on the option.
Generalize this option type, which is a timestamped list of
<line number>|<arbitrary string>. That way this type is not strongly
coupled with the flag-lines highlighter, and can be reused for other
use cases.
range-faces are now used to replace-range highlighters, where the string
part is not interpretted as a face but as a display line, so the name was
not relevant anymore.
Add a ranges highlighter that takes a timestamped list of ranges and
associated face. Add a spell.kak file that uses aspell pipe interface
to fill a range-faces option.
