Add operator[] to WayNodeList.
Add test helper function.
Geometry handling refactored and extended.

There are now factories for creating WKT, WKB, and OGR geometries. Currently
they can create POINTs from Locations/Nodes and LINESTRINGs from WayNodes/Ways.

There are extensive tests for WKT geometries, but none for WKB and OGR.

The example program osmium_toogr has been changed to use the new way of doing
things.

The geometry creation framework can be extended to handle other kinds of
geometries (like GEOS) with minimal effort.