Add Configuration.from_yaml method

Author: rmk135

docs/main/changelog.rst

@@ -9,6 +9,7 @@ follows `Semantic versioning`_
 
 Development version
 -------------------
+- Add ``Configuration.from_yaml()`` method to load configuration from yaml file.
 - Add ``Configuration.from_ini()`` method to load configuration from ini file.
 - Add ``Configuration.from_dict()`` method to load configuration from dictionary.
 - Remove undocumented positional parameter of ``DependenciesContainer`` provider.

setup.py

@@ -40,9 +40,11 @@
       url='https://github.com/ets-labs/python-dependency-injector',
       download_url='https://pypi.python.org/pypi/dependency_injector',
       install_requires=requirements,
-      packages=[
-          'dependency_injector',
-      ],
+      extras_require={
+          'yaml': [
+              'pyyaml',
+          ],
+      },
       package_dir={
           '': 'src',
       },