* java_keystore: add `certificate_path` and `private_key_path` options
* Update DOCUMENTATION and EXAMPLES accordingly.
* Refactor integration tests to play the same tasks twice.
* Add a changelog fragment (minor_changes).
refactor DOCUMENTATION
* Add useful info for better understanding of what options allow
keystore regeneration on the fly, and what other options lead the
module to fail, if their values change.
* Fix indentation and tenses.
* Add myself as author.
* readability-related stuff + changelog fragment
