hll benchmark
remove HLL version specific code outside of HyperLogLogCollector
no need for volatile references

we make no guarantees wrt threadsafety in this class
minor hll optimizations
check should be safe to move out of loop
make it clear mergeAndStoreByteRegister has no side effects
clean up + header
mark long-running tests as @Ignore + docs
one more final variable for good measure
folding into direct buffers is faster
benchmark more closely matches actual implementation
Merge pull request #441 from metamx/hll-optimization

HyperLogLog optimizations and benchmark