consistency between input spans and getCoordinates

[NEW] Map class get's a getCoordinates() method. It chekcs the self.Reverse
    property for establishing how to order start/end values in the returned
    series. _Annotatble.getCoordinates() method now uses this method on Map.
[FIXED] On reverse strand _Feature, getCoordinates() did not return a value
    that was usable. Instead of [(end, start), ..] you got [(start, end), ..].
    The latter could not be used to recreate the _Feature. This is now fixed.