PR for Release 0.6.0

Goals for this release:

- [x] Place words into arbitrary shapes, via image masks. _Done: https://github.com/danbernier/WordCram/pull/32._
- [ ] Write to SVG files, instead of just outputting to the Processing sketch. This is almost done; see https://github.com/danbernier/WordCram/pull/23.
- [ ] A fix for [Issue #30](https://github.com/danbernier/WordCram/issues/30), "How to include Stop words?"
- [ ] When re-rendering a WordCram, don't reload web URL downloads - cache them on the file system. See https://github.com/danbernier/WordCram/issues/17.
- [ ] Put in some kind of observer interface, so you can get progress feedback as your sketch runs. See particularly https://github.com/danbernier/WordCram/pull/32#issuecomment-20315871.
- [ ] Fix for Right-to-Left languages. See #37.