This non-modifying function returns a new Bitset
object of the same maximum size as the original but which only contains
those values at the indices specified by the argument other.
Indices in other may be specified either as a vector of logicals, a
vector of integers or as another bitset. If a vector of logicals is
specified, it must be of the same size as the bitset. Please note that
filtering by another bitset is not a "bitwise and" intersection, and will
have the same behavior as providing an equivalent vector of integer indices.
filter_bitset(bitset, other)