Extension conforming CLLocationCoordinate2D to the Equatable protocol

#Includes:

• an extension to type CLLocationCoordinate2D to conform to Equatable
• an extension to type Double to truncate a geo-coordinate to a specified number of decimal places.

#Reasoning:  If two coordinates are queried for approximate equality, their latitude and longitude need to be of predictable length. A value in decimal degrees to 5 decimal places is precise to 1.1132 meter at the equator. Close enough for my purpose.

#Use Case: Compare two arrays of coordinates for matches.

#Implementation: a function taking two arrays of coordinates as parameters and returning an array wrapped in an optional:

func  findCommonCoordinates(_ lhs: [CLLocationCoordinate2D], _ rhs: [CLLocationCoordinate2D]) -> [CLLocationCoordinate2D]?
{
  var coords = [CLLocationCoordinate2D]()

    for lhsItem in lhs {
      for rhsItem in rhs {
        if lhsItem.latitude == rhsItem.latitude
          && lhsItem.longitude == rhsItem.longitude {
            coords.append(lhsItem)
          }
      }
    }
  return coords
}