Two cuckoos in the voting nest

[Libbum]

The current bloom filter implementation for voters is restrictive. The voting system need to be rewritten such that voters is removed from the database, and likes & dislikes become BLOB types which house a cuckoo filter in each. That way we can add and delete voters from one or the other and allow users to change their minds on their vote.

This can't happen yet as rust-cuckoofilter currently has no export of its important internals. I'll have a chat with the authors and investigate an implementation. Until then, we'll put this in v0.3. It could be moved up though.

[Libbum]

I've implemented the interop here, PR here; so we can move this up to v0.2.

[Libbum]

The work we've done on the cuckoofilter is ready and just waiting for seiflotfy to push v0.4 to crates. Should be there any time now.