How should IMDReader handle connection refused?

[ljwoods2]

If reader raises ConnectionRefusedError in first iteration, protoreader's next() catches it since ConnectionRefusedError is an IOError

    def next(self) -> Timestep:
        """Forward one step to next frame."""
        try:
            ts = self._read_next_timestep()
        except (EOFError, IOError):
            self.rewind()
            raise StopIteration from None

How will the user know they never connected to the gromacs server? Can we just issue a warning?

[ljwoods2]

One solution is to start the simulation in reader's init(). #7 does this