Feature/fix NC, NIR

* NC and NIR now use the #copy_whole_raster_band function to copy data from their original.  This seems more complete/thorough than converting to an array, then writing the array.
* OGR error handling, mapping OGRErr constants to Ruby exceptions.
* Added CPLErr handling where it was previously missing.
* Somehow, some time ago I'd managed to add `*.rb` to the .gitignore (!!!) _and_ managed to not notice missing files from my check-ins.  Amazing.  Anyway, added those files back in.