* Replace InventoryFileCacheModule with a better developer-interface
Use new interface for inventory plugins with backwards compatibility
Auto-update the backing cache-plugin if the cache has changed after parsing the inventory plugin
* Update CacheModules to use the config system and add a deprecation warning if they are being imported directly rather than using cache_loader
* Fix foreman inventory caching
* Add tests
* Add integration test to check that fact caching works normally with cache plugins using ansible.constants and inventory caching provides a helpful error for non-compatible cache plugins
* Add some developer documentation for inventory and cache plugins
* Add user documentation for inventory caching
* Add deprecation docs
* Apply suggestions from docs review
* Add changelog
* Move ansible.compat.tests to test/units/compat/.
* Fix unit test references to ansible.compat.tests.
* Move builtins compat to separate file.
* Fix classification of test/units/compat/ dir.
