Rasterio

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- The _CRS class has been refactored so that a WKT representation, rather than
PROJ4 representation, is the canonical form. This resolves issues 1397 and
1587 specifically, and an entire category of issues discussed in
https://rasterio.groups.io/g/dev/message/68.
- Native support for Google Cloud Storage using "gs://" URLs has been added
(1577).
- On entering a dataset context (DatasetBase.__enter__) a new anonymous GDAL
environment is created if needed and is entered. This makes `with
rasterio.open(...) as dataset:` roughly equivalent to `with
rasterio.open(...) as dataset, Env():`. This helps prevent bugs when datasets
are created and then used later or are used in different scopes.

-------------------

- Fix a buffer dttype mismatch on Windows introduced in 1.0.12 (1579).

-------------------

- Rasterio's lower level I/O functions now take Py_ssize_t index arrays and
will raise exceptions for type mismatches instead of swallowing the
exceptions (1076).
- The _boundless_vrt_doc function's background layer no longer needs an
in-memory dataset and the performance regression noted in 1499 has been
reversed. We've also found a performance improvement in masked boundless
reads in the case that the source data is entirely valid.
- The signature of the private _boundless_vrt_doc function in rasterio.vrt has
changed. Its background keyword argument now takes an int or float, a new
masked keyword argument has been added, and the function returns a unicode
str instead of ascii-encoded bytes.
- The copy and copyfiles functions of rasterio.shutil now raise an exception
when the source and destination paths identify the same dataset (1569).

-------------------

- Prevent needless warning when making boundless reads with a fill value
(1499).
- The GDAL band cache is flushed at the top of build_overviews to fix 1497.
- Options --gdal-data and --proj-data have been added to the rio-env command so
that users of Rasterio wheels can get paths to set GDAL_DATA and PROJ_LIB
environment variables.
- The attempt to make GDAL and PROJ support file discovery and configuration
automatic within methods of the CRS class has been reverted. Users must
execute such code inside a `with Env()` block or set the GDAL_DATA and
PROJ_LIB environment variables needed by GDAL.

-------------------

- Avoid segmentation fault when OSRGetAuthority* functions return null
pointers, making Rasterio more robust when reading CRS that don't map
perfectly to PROJ.
- Ensure that GDAL and PROJ support files can be found in Rasterio wheels when
we call CRS methods (1539).
- Accomodate the Esri flavor of projection WKT (1537).
- Add missing raster offsets and scales properties (1527).

------------------

Bug fixes:

- Delegate test of the environment for existing session credentials to the
session class to generalize credentialization of GDAL to cloud providers
other than AWS (1520). The env.hascreds function is no longer used in
Rasterio and has been marked as deprecated.
- Switch to use of botocore Credentials.get_frozen_credentials (1521).
- Numpy masked arrays with the normal Numpy mask sense (True == invalid) are
now supported as input for feature.shapes(). The mask keyword argument of the
function keeps to the GDAL sense of masks (nonzero == invalid) and the
documentation has been improved to communicate this (1517).
- The defaults for WarpedVRT's `src_nodata` and `nodata` keyword arguments are
no longer None, but are markers for the default behavior: inheritance of
nodata values from the VRT's source dataset. Values of `None` for these
keyword arguments means that the VRT does not inherit from the source and has
no nodata value at all (1503).
- WEBP has been added to the Compression enum. Exploitation of this new
compression mode will require GDAL 2.4.
- Rasterio now check for two AWS environment variables before creating a
session (1494).
- The ensure_env_with_credentials decorator which wraps rasterio.open will no
longer clobber the credentials in a surrounding environment or seek
credentials when they already exist (1507).
- The comparison of CRS objects to dicts and strs that we pledged to remove at
1.0 has at last been removed (1492).