Kakoune now does not touch cursors when scrolling. It checks
if either the buffer or selections has been modified since
last redraw.
Fixes#4124Fixes#2844
Add support for a third color in face definition that controls
the underline and a 'c' attribute for curly underline (that takes
precedence over 'u' if both are specified)
Allow empty colors to mean default, so that `,,red+u` means the
same as `default,default,red+u`
Fixes#4138