Add more multipolygon test cases
Add multipolygon wkt files

They show what the multipolygons are supposed to look like. They are also added
to the grid.db file and the QGIS project.
WKT file reorganization
Remove empty ways.wkt and nodes.wkt files
Add scripts to generate (nodes|ways).wkt from data.osm

This will not always to the right thing, so you have to check the output.
Remove duplicate coordinates when generating ways.wkt file
Add to README.md