message: Disallow warnings in doctests.
diff: #![crate_type = "lib"]
  // Enable `doc_cfg` features when `docsrs` is defined by docs.rs config
  #![cfg_attr(docsrs, feature(doc_cfg))]
  +#![doc(test(
  + attr(deny(warnings), allow(dead_code, unused_variables))
  +))]
  //! # GDAL
  //! [GDAL](http://gdal.org/) is a translator and processing library for various raster and vector geospatial data formats.
  