Serialisation/deserialisation. Fixes #2

Added code to convert a bloomfilter to a Array of bytes and reconstruct
a bloomfilter from such an array.

I am not a very experienced Javascript programmer and I am looking forward to comments about stylistic and technical problems with my code.

In particular there seem to be different ways of representing binary data: 
http://blog.n01se.net/blog-n01se-net-p-248.html
I like the array of bytes better than the unicode string, but on the other hand things like window.btoa seem to expect an unicode string.