Using generics, allowing to switch transparently between uint8 and
uint16 for the fingerprint size.

Performance neutral according to benchmarks

~/goworkspace/bin/benchstat ~/master.benchstats ~/generics.benchstats
name             old time/op  new time/op  delta
Filter_Reset-4   10.0µs ± 0%   9.9µs ± 0%   ~     (p=1.000 n=1+1)
Filter_Insert-4  18.2µs ± 0%  18.0µs ± 0%   ~     (p=1.000 n=1+1)
Filter_Lookup-4  1.52µs ± 0%  1.51µs ± 0%   ~     (p=1.000 n=1+1)

Instead of using multiple methods for instantiating a filter for a
chosen precision.

There is no asymptotic advantage to try both idx & alt idx for an item
to insert. Rather just let cuckoo kickout do it's thing.

Avoids some unnecessary ifs in the implementation.

By seeding random source.

Previously, items only moved to the alternative index on cuckoo inserts.

Plus a tiny rename.