adding a x::ctrl() example

__qpu__ void ccnot(qreg q) {

  // set initial state to 111

  X(q);

  X::ctrl({q[0], q[1]}, q[2]);

  Measure(q);

}

int main() {

  // allocate 3 qubits

  auto q = qalloc(3);

  ccnot::print_kernel(std::cout, q);

  // Run the unitary evolution.

  ccnot(q);

  // should see 011 (msb) for toffoli input 111

  q.print();

}