Allow range to return ints if all args are ints

[emlyn]

This change makes the range function return integers if all arguments are integers.

I don't think this should break anything, since the values returned should be unchanged,
and I think integers should be accepted anywhere floats are expected.

This would allow things like the following to work:

live_loop :foo do
  sample "drum", range(2, 6).tick
  sleep 0.5
end

Currently that fails with an error like: Unknown sample filter type: Float - got: 2.0 (RuntimeError),
which can cause confusion (see e.g. https://in-thread.sonic-pi.net/t/force-integer-from-a-range/8625/1).