GC-45: Update copyright information:

- Changes to code base were previously done in 2020 as well (based on
git history).

GC-45: Drop support for Python 3.5, 3.6, and 3.7:

- Updated documentation, removing references to versions as being
supported.
- Switched the Vagrant test machine to Debian Bullseye (still in LTS
support) to match the main development environment.
- Updated functional tests for output changes in OpenSSL CLI from
Debian Bullseye.
- Updated Tox configuration and instructions.
- Dropped workaround for Python 3.5.
- Updated package requirements.
- Updated release notes.

GC-39: Added support for Python 3.9:

- Updated release notes
- Updated functional test for changes in help output in Python 3.9.
- Updated comments on public signing keys used for validating the
Python archives when using Vagrant provisioning.
- Updated supported Python versions in package configuration file.
- Updated Python versions used for tests.

GC-37: Added support for requesting custom RSA key size when issuing server certificates:

- Added functional test.
- Added unit tests.
- Added new CLI option to the server command.
- Updated the server command to use the passed-in key specification.
- Updated existing tests to cope with changes to the server command
function signature.

GC-37: Rename the test for server key specification:

- The test should be able to cover all of the server command-related
key specification functionality.

GC-23: Removed option to update DNS names from server command:

- Removed functional test.
- Dropped the option from CLI.
- Dropped the option from command function implementation.
- Updating code for new command function signature.
- Updated existing unit tests.
- Removed unneeded unit tests.

GC-19: Updated server --update-dns-names implementation to inform user about unchanged private key:

- Updated functional and unit tests.
- Updated message shown to user when using --update-dns-names server
option to include information about private key remaining the same.

GC-19: Added option for updating server certificate DNS names:

- Added functional test covering the new scenario.
- Added option to server command for updating DNS names for already
issued certificate. Private key is kept for this purpose.
- Implemented unit tests.
- Fixed functional test related to viewing short usage instructions.

GC-15: Prevent server command from overwriting artifacts and clean-up incorrect CLI tests:

- Added functional test for scenario where a server certificate has
already been issued.
- Updated server certificate issuance command not to overwrite the
artifacts.
- Fixed a couple of both server and init tests related to CLI parsing
to not create artifacts unless necessary, and if necessary to create
artifacts in temporary (test) directory. Otherwise intermittent
failures will happen.

GC-15: Implemented functionality for including extra DNS names in server certificates:

- Added functional test covering the new scenario.
- Updated invocations of relevant commands in existing code to pass-in
the list of extra DNS names where appropriate.
- Updated server command and high-level function for issuing server
certificates to accept list of additional DNS subject alternative
names to include in certificate.
- Fixed existing unit tests.
- Added additional unit tests that cover the new function.

GC-15: Implemented functionality for issuing a server certificate:

- Added functional test covering the user scenario.
- Updated CLI implementation to show user message about issued server
artifacts.
- Implemented functionality in the server command.
- Fixed a small typo in docstring for issue_certificate function.
- Implemented high-level crypto function for issuing server
certificates.
- Implemented additional storage functions for reading an entire CA
hierarchy, individual private keys, and individual certificates.
- Implemented the necessary unit tests covering newly implemented
code.

GC-15: Implemented scenario for server certificate issuance where user has not initialised the CA hierarchy:

- Added functional test that tests if correct error is shown to user
in case he/she has not initialised the CA hierarchy.
- Introduced new function to check if storage is initialised.
- Added initial simplified server command implementation.

GC-15: Added server command parser:

- Added functional test for testing new command presence and help.
- Added initial parser implementation.