Fix for #39: Set twofishes' JVM heap size to larger default

I tried a few times to use a lower default than 1500MB on an m1.medium, but didn't have any luck. Even 900MB was too little for twofishes to start up without an OOM. I added a note recommending at least an m1.large in the developerdocs. It's possible that someone with more JVM-fu than me might be able to revise it.