Add type() function to OSM entities. Put string symbols as globals.
Refactoring: Pull out more string symbols into globals.
Refactoring: Get rid of some unnecessary shared_ptrs.
Add convenience functions for converting to spatialite.
Add support for multipolygons.

Add wrapper code needed to access libosmiums multipolygon assembly code.
Also extends "converter" convenience functions to detect automatically
whether multipolygon assembly is needed and do the right thing.
Cleanup of includes.
Make sure destructors of wrapper classes are all private.

Wrapper classes should not be destructed willy-nilly, so that v8 doesn't get
confused.
Rename some variables with bad names.
Add helper function for creating v8 externals with wrappers in them.

Also adds missing "area" case in buffer iterator.
Make converter more flexible and function names descriptive.
Add Reader.read_all() function to read while file in one go.
Add functions to filter data in buffer valid at point in time.

var date = new Date();
var filtered_buffer = buffer.filter_point_in_time(date);
Ignore broken geometries in converter.
Converter can also work with buffer instead of file.