Enhanced Avoid and added Available

- Added ferries to avoid.
- Changed Avoid to [Flags], so that you can combine e.g. toll and ferries to avoid. e.g. request.Avoid = Avoid.ferries | Avoid.tolls;
- Made Avoid available to DirectionRequest
- Added Alternatives property to DirectionRequest
- Fix to DirectionService constructor (it ignored the baseUrl)
- Added Maneuver Property to DirectionStep.