lift Clone constraint on type H

[gwy15]

Hello,

I noticed that HLL and HLL+ implements Clone using derive. Default compiler implementation requires that H implements Clone for HyperLogLogPF<H, B> and HyperLogLogPlus<H, B>. This is unnecessary since only hashes are used and type H is merely used as type check.

This PR lifts the Clone constraint on type H by implement Clone mannually rather than using derive.

It is useful when working with types like HyperLogLogPF<str>.