Window: forget timestamp when options changes
Simplify FlagLines, do not try to update the option
RegexColorizer maintains a per buffer cache
Do not pass a window to highlighters factories
rework cpp indenter, try to make them more readable
indent fixes
fixup cpp.kak
Add support for defining and referencing highlighters

* defhl <name> defines a shared highlighter
* addhl -def-group <name> adds highlighters to the defined highlighter
* addhl ref <name> add the defined highlighter to the window's ones
Change rc files to use shared highlighters
README: document shared highlighters
Write errors while sourcing a file in the debug buffer
Add basic region highlighter
use region highlighter for cpp