Data is not being stored in binary format

[SidHarder]

Currently this implementation of https://github.com/ipfs/interface-pull-blob-store works fine however it can't be used to help solve this ipfs/js-ipfs-repo#111. The go implementation saves the values of keys as binary data in the LevelDb store. This implementation does not store the values as binary. It is trivial to store the values as binary but then the tests do not pass. I will be working on solving this in the next few days.

[SidHarder]

concatenated the incoming array of buffers into one buffer and configured level value encoding to binary.