contrib/debian/compat

templater: add separate() template function

A pretty common pattern in templates is adding conditional separators
like so:

  {node}{if(bookmarks, " {bookmarks}")}{if(tags, " {tags}")}

With this patch, the above can be simplified to:

  {separate(" ", node, bookmarks, tags)}

The function is similar to the already existing join(), but with a few
differences:

 * separate() skips empty arguments

 * join() expects a single list argument, while separate() expects
   each item as a separate argument

 * separate() takes the separator first in order to allow a variable
   number of arguments after it

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