Initial, working version.
Clear highlight more or less on next keypress.
Factor all the yanking stuff into its own set of methods.
Work with yanked lines, and work around the fact that both Visual and Normal modes will ahve  their own versions of m_highlightedYank.
Use savedLineColor() instead of searchHighlightColor() - not sure if this is an improvement, but I'll store it just in case :)
Rename 'clearYank' to 'clearYankHighlight'.
Don't use the absolute path to the syntax highlight file in the 'cache' entry name - it causes problems when the cache is generated using emscripten-kate-native and read in in ordinary emscripten-kate.  Trim off the leading directories.  The pre-generated cache entries have been updated accordingly.
Merge in the 'yank highlight' branch.