dealing with the tricky case where multiple address points are in the same location, so there's no use in making seperate address nodes. fortunately the shapefile gives us "P" and "S" to denote primary and secondary addresses, so we can prefer the primary one. In the case where the address points are in unique locations, we still produce two OSM nodes. Also, do some rounding because the data had noise at the sub-micron level (so many decimal places!)