Move as_file to the global namespace and update documentation accordingly. Closes python#86.

Author: jaraco

importlib_resources/__init__.py

@@ -3,12 +3,14 @@
 import sys
 
 from ._compat import metadata
+from .trees import as_file
 
 
 __all__ = [
     'Package',
     'Resource',
     'ResourceReader',
+    'as_file',
     'contents',
     'files',
     'is_resource',

importlib_resources/docs/using.rst

@@ -155,8 +155,7 @@ to this temporary file as a :py:class:`pathlib.Path` object.  In order to
 properly clean up this temporary file, what's actually returned is a context
 manager that you can use in a ``with``-statement::
 
-    from importlib_resources import files
-    from importlib_resources.trees import as_file
+    from importlib_resources import files, as_file
 
     source = files(email.tests.data).joinpath('message.eml')
     with as_file(source) as eml: