Securesystemslib

* Add support for *OpenPGP* EdDSA/ed25519 keys and signatures (188)
bump

* Remove unnecessary `python-dateutil==2.8.0` version pinning to not cause
downstream dependency conflicts (192)

* Fix stream duplication race conditions in subprocess interface (186)

* *backwards incompatible*
* Remove data serialization in `create_signature` and `verify_signature` (162)
* Replace mostly obsolete `TempFile` utility with single helper function (181)
* Remove *TUF*-specific code and comments (165)
* *new features*
* Add support for *pkcs1v15* RSA signature scheme and additional hash algorithms (173, 175)
* Add basic *OpenPGP* support, transferred from [in-toto](https://github.com/in-toto/in-toto) (#174, 176, 185)
* *miscellaneous*
* Fix publishing of code coverage and enhance test configuration (171)
* Make colorama a strict dependency (178)
* Enhance source distribution metadata (168)
* Update downstream Debian metadata (177)

* Provide option to normalize line endings (`\r\n` -> `\n`, `\r` -> `\n`) when
calculating the hash of a file (default: do not normalize).
* Update developer dependencies (dev-requirements.txt):
* cryptography 2.2.2 to 2.3.1
* tox 3.0.0 to 3.2.1

* No (en|de)cryption of ed25519 key files when given empty password (pr 148).

* Support ed25519 crypto in pure python with default installation (pr 149).

* Update installation instructions to indicate commands needed to install
optional dependencies for RSA and ECDSA support (pr 150).

* Edit setup.py's license classifier to `OSI LIcense :: MIT` (pr 151).