title: Rescale Y-axis in Highcharts after zoom while maintaining zoomType=x behavior
body: <p>I have a time series chart in Highcharts where I would like users to be able to zoom in on specific date ranges. This is possible by setting <code>zoomType: 'x'</code>. However, once the chart is zoomed, the Y-axis does not rescale to best fit the visible data. For instance, if the original Y-axis runs from 0 to 100, and I zoom on an area with data that only runs 91 to 99, then I probably want the Y-axis to change to be 90 to 100 or something similar. Basically, I want figure out how to get Highcharts to re-run its axis-scaling logic considering only the visible data.</p>
  
  <p>A halfway measure is to set <code>zoomType: 'xy'</code> which allows the user to draw a rectangle and zoom on that rectangle. However, this is inconvenient for the user in this context, as all they really want to be able to do is isolate a date range and then study the variation in the data in that range.</p>