New features for upcoming version 4

[lonvia]

This adds the API changes and new features for the upcoming new major version:

• persistent OSM objects: handlers can now add information to objects to be used by later handlers
• new filters: TagFilter, EntityFilter, IdFilter (#218), GeoInterfaceFilter (#11)
• improved SimpleWriter
  • can be used as a Handler
  • can be used as context manager
  • new overwrite parameter to automatically overwrite files
  • generic add() function that takes any object
• improved FileProcessor
  • allow separate filters for area processing
  • new handler for filtered objects
• new BackReferenceWriter and ForwardReferenceWriter which automatically complete file with referenced objects
• expose osmium's IdSet
• new haversine function for two points

Documentation and usage examples fof these new features to follow.