message: prepare for 0.6.0 release
diff: # Changes
  +## 0.5.0
  +
  +* [Bump geo-types from 0.3 -> 0.4](https://github.com/georust/gdal/pull/71)
  +* [Allow reading block-size of Rasters](https://github.com/georust/gdal/pull/67)
  +* [Add prebuilt-bindings GDAL 2.3 and GDAL 2.4](https://github.com/georust/gdal/pull/69)
  +* [Make GdalType trait public](https://github.com/georust/gdal/pull/66)
  +* [RasterBand to Ndarray, with failure](https://github.com/georust/gdal/pull/68)
  +
  ## 0.4.0
  * [Migrate to the `geo-types` crate](https://github.com/georust/gdal/pull/60)
  * [Replace `error-chain` with `failure`](https://github.com/georust/gdal/pull/58)
  