That means we can now have highlighters active at global, buffer, and
window scope. The add-highlighter and remove-highlighter syntax changed
to take the parent path (scope/group/...) as a mandatory argument,
superseeding the previous -group switch.
Client quitting no longer immediately unwinds, client is just pushed
for deletion until we get back to the main loop, similarly to what
happens for buffer and window deletion.
That way we get proper unicode support in regular expressions as long
as the current locale treats wchar_t as unicode codepoints.
Fixes#638Fixes#595Fixes#162
