The splitter in question was depending on
github.com/silvasur/buzhash which is not licensed according to FOSSA bot
Switched to new faster implementation of buzhash, which is
unfortunately incompatible and will split the objects in different
places.
This change is be semi-breaking - old repositories can be read, but
when uploading large objects they will be re-uploaded where previously
they would be de-duped.
Also added 'benchmark splitters' subcommand and moved 'block cryptobenchmark'
subcommand to 'benchmark crypto'.
