Convert creation option values to strings.
Convert creation option values to strings.

Closes #76.

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