Please add support for polygonal annotations.

[jwilk]

Issue reported by @jsbien:

I'm specifically interested in triangular annotations approximating the shape of the insertion editorial mark and linking a place in a text to the appropriate element of an errata.

[jwilk]

Unfortunately, I don't have time to implement any new features in djvusmooth. Code contributions from other people are of course welcome.

[jwilk]

Duplicate of #4.

[jwilk]

Comment submitted by @jsbien:

I've just learned that polygonal annotations are supported by an Emacs djvu package (http://elpa.gnu.org/packages/djvu.html), but I had no time yet to check if this really works. If it does, then from my point of view the problem is solved.