many improvements, fully backwards compatible...

- gitignore: Remove xcuserdata/ directories from repository
- OCAlgorithms: had a warning in my XCode 5.1.1 and fixed it.
- OCDistance: made algorithm for calculating the distance more accurate and changed its unit to actual meters (the old algorithm got more and more inaccurate when you move away from the equator)
- OCDistance: added functions that are needed to check if a point is contained within a region; and another algorithm to check wether a region is fully contained within another region. (the algo is a bit more complex than for CGRect, because numbers do wrap around. The coordinates are not real numbers but values of the field Z/180 and Z/360.)
- OCMapView: changed the type of the clusterSize property to float, because CLLocationDistance is reserved for actual distances that are independent of the current zoom level.
- OCMapView: defers clustering asynchronously to the main loop to improve performance considerably for the use case where you call -addAnnotation: multiple times instead of calling just -addAnnotations: once. (analogous to -setNeedsDisplay: vs. -display from UIView)
- OCMapView: changed many properties to iVars, because the performance of iVars is much much better. KVO-compliance is kept for all public properties though.
- OCMapView: made -filterAnnotationsForVisibleMap: more accurate while improving performance.