0.0.30 Release

• BUG: Fix assigning fill value in rio.pad_box (pull #140)
• ENH: Add rio.write_transform to store cache in GDAL location (issue #129 & #139)
• ENH: Use rasterio windows for rio.clip_box (issue #142)
• BUG: Add support for negative indexes in rio.isel_window (pull #145)
• BUG: Write transform based on window in rio.isel_window (pull #145)
• ENH: Add rio.count, rio.slice_xy(), rio.bounds(), rio.resolution(), rio.transform_bounds() to Dataset level
• ENH: Add rio.write_coordinate_system() (issue #147)
• ENH: Search CF coordinate metadata to find coordinates (issue #147)
• ENH: Default rio.clip to assume geometry has CRS of dataset (pull #150)
• ENH: Add rio.grid_mapping and rio.write_grid_mapping & preserve original grid mapping (pull #151)