Use importlib.metadata rather than pkg_resources for version metadata

setup.cfg

@@ -7,7 +7,7 @@ select = B,C,E,F,W,T4,B9
 
 [isort]
 known_first_party=xbatcher
-known_third_party=numpy,pkg_resources,pytest,setuptools,sphinx_autosummary_accessors,tensorflow,torch,xarray
+known_third_party=numpy,pytest,setuptools,sphinx_autosummary_accessors,tensorflow,torch,xarray
 multi_line_output=3
 include_trailing_comma=True
 force_grid_wrap=0

xbatcher/__init__.py

@@ -1,11 +1,11 @@
-from pkg_resources import DistributionNotFound, get_distribution
+from importlib.metadata import PackageNotFoundError, version
 
 from .accessors import BatchAccessor  # noqa: F401
 from .generators import BatchGenerator  # noqa: F401
 from .util.print_versions import show_versions  # noqa: F401
 
 try:
-    __version__ = get_distribution(__name__).version
-except DistributionNotFound:  # noqa: F401; pragma: no cover
+    __version__ = version(__name__)
+except PackageNotFoundError:
     # package is not installed
-    pass
+    __version__ = 'unknown'

xbatcher/_version.py

@@ -0,0 +1,7 @@
+from importlib.metadata import PackageNotFoundError, version
+
+try:
+    __version__ = version(__name__)
+except PackageNotFoundError:
+    # package is not installed
+    __version__ = 'unknown'