[NTG-context] drops module update

Hi, just a small maintenance update (everything was broken) for the drops module. Should be working again with the latest versions of ImageMagick (6.9.2-0+) and ConTeXt (luatex 0.85.0+). Files (version 2016-01-18) can be found here [the zip file also contains the documentation (drops.pdf)] https://spideroak.com/browse/share/indiego/public/ConTeXt/drops/ Have fun, Peter