title: Zoom MKMapView to fit polyline points
body: <p>I have an array, allCollections, that holds programmatically-created arrays of CLLocations the user has recorded through my iOS app. Each sub-array in allCollections holds all the location points in a trip taken.</p>
  
  <p>I draw MKPolylines off of the CLLocations in the arrays in allCollections to represent those trips on an MKMapView. My question is this: With the polylines added to the map, how would I go about programmatically zooming and centering the map to display all of them?</p>