renderLineStyle is now an array of style arrays
cMonScroll function added to move scroll position of other pane to match
The on('renderLine') event now covers all lines, a change since earlier
versions of CodeMirror
This means a reworking of code was needed here to firstly identify a
matching pane and then if we have a match, add the style. Done in a for
loop and considers array items in renderLineStyle
Reworked much of the updateDiffs functin to reset array & value to begin
with and push to renderLineStyle array now. Also only doing this if we
have a height higher than normal to set, for perf reasons
No need to set renderLineStyle to false anymore
Finally, sorted the order things happen into 2 logical sections - main
pane changes first then diff pane changes after
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