help: add example of '[templates]' usage V2: - move from shortest() with minlength 8 to minlength 4 - mention [templates] in config.txt - better describe the difference between [templatealias] and [templates] V3: - choose a better example template

exchange: correctly specify url to unbundle (issue5145) This parameter is slightly confusingly named in wireproto, so it got mis-specified from the start as 'push' instead of the URL to which we are pushing. Sigh. I've got a patch for that which I'll mail separately since it's not really appropriate for stable. Fixes a regression in bundle2 from bundle1.