Generalized output for vectors/bitvectors

Now it's also possible to output the contents
of compressed bitvectors and intvectors like
that:

rrr_vector<> bv = bit_vector{1,0,1,0,0,1,0};
cout << bv << endl;

enc_vector<> ev = int_vector<>{1,2,3,4,5,6,7,9};
cout << ev << endl;