Add Symfony Deprecation Contracts package

- Created CHANGELOG.md to maintain version history.
- Added README.md with usage instructions for the trigger_deprecation() function.
- Initialized composer.json for the Symfony Deprecation Contracts library, specifying dependencies and autoloading.

modules/pshowsso/deps/league/oauth2-github/.gitignore

@@ -0,0 +1,5 @@
+/build
+/vendor
+composer.phar
+composer.lock
+.DS_Store