BUG: Update rss extension

    fix a bug: the mask image is not init-ed to all 0, which causes problem

    fix a bug: mistake in computing kappa

    clean up some debuging code

compare view:

https://github.com/gaoyi/RSSExtension/compare/d447085b3955abb460a8c39e48af925132dd8920…2be89dfac932bfae034ee43c87b6383782c1fb33