Taking an external dependency just to convert ints to byte arrays
is somewhat of a waste, especially when Rust isn't very aggressive
about doing cross-crate LTO.
Note that the latest LLVM pattern-matches this, and while I haven't
tested it, that should mean this means no loss of optimization.
* add client side block filters with code from murmel. use siphash from bitcoin_hashes pass Bitcoin Core tests upgrade to bitcoin_hashes 0.7
* add filter.filter_id() test use BlockFilter directly
* fixed edge cases of matching empty query sets or or using empty filter