Limit number of splits to 1.
Limit number of splits to 1.

Closes #254.

brendan-ward/rasterio,kapadia/rasterio,brendan-ward/rasterio,njwilson23/rasterio,youngpm/rasterio,johanvdw/rasterio,perrygeo/rasterio,kapadia/rasterio,youngpm/rasterio,njwilson23/rasterio,njwilson23/rasterio,johanvdw/rasterio,kapadia/rasterio,perrygeo/rasterio,youngpm/rasterio,brendan-ward/rasterio,perrygeo/rasterio,sgillies/rasterio,clembou/rasterio,clembou/rasterio,johanvdw/rasterio,clembou/rasterio