Poor bugfix in bb98 function

[unicornsasfuel]

I have no idea why, but as mentioned in #44 the bb98 algorithm as implemented would incorrectly identify the last bit of the message. Oddly, it also seems to have about 9 bytes of random junk at the beginning too. I've applied a hacky fix which just brute forces the correct message by waiting until the set of potential plaintexts is small enough to brute force reasonably, then does so. This provides a small performance increase, but I have no idea why this fix is necessary and as such it should be fixed properly.