GC-45: Update copyright information:

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

GC-37: Use KeyGenerator instead of generate_private_key in unit tests:

- Replaced all uses of generate_private_key with KeyGenerator
invocations that explicitly request 2048-bit RSA.

GC-37: Refactor key specification handling:

- Perform the key specification parsing within CLI module itself,
don't do it via crypto module.
- Pass-in tuple consisting out of algorithm and associated parameters
into the init command instead of key generator.
- Updated all tests to accomodate the change in init function
signature.
- Simplify the KeyGenerator class.
- Do not test if KeyGenerator class sets the properties via
constructor - it is sufficient to test string represenation and key
generation.

GC-37: Added support for requesting custom RSA key size when initialising the CA hierarchy:

- Added functional test.
- Added unit tests.
- Added new CLI option for specifying the algorithm.
- Implemented KeyGenerator factory-like class that can be called to
generate a private key with desired specification.
- The init init function now accepts a callable that is used to
generate private keys.
- The generate_ca_hierarchy function now accepts a callable that is
used to generate private keys.
- Updated existing unit tests to cope with changes to the init
and generate_ca_hierarchy function signatures.
- Updated existing unit tests to cope with changes to existing
functionality.
- Updated existing functional tests to cope with changes in command
output.

Noticket: Compatibility fixes for Python 3.4:

- Fixed invocation of pexepect.spawnu to convert the passed-in
arguments explicitly into a list. Necessary since Python 3.4 can't
use the *args construct outside of assignment.
- Updated the certificate_to_pem function to return str instead of
bytes. Necessary since Python 3.4 does not support things like b"%s"
% mybytes.
- Fixed test for existence of help CLI command. Previous code was
referencing a wrong/non-existent function help (the actual name has
to be help_ in order not to shadow the built-in function).
- Updated unit test invocations that use the read_certificate
function.
- Updated tests for the read_certificate function.

GC-22: Implemented issuance of client certificates using passed-in CSR:

- Added functional test covering the issuance of client certificate
using CSR.
- Updated default value for the CSR client command option to be
explicitly None.
- Updated the client command to take in the CSR as an argument and
process it accordingly.
- Added helpers for generating CSR, as well as writing and reading
them to/from file.
- Updated existing tests to use new signature for the client
command.
- Added new unit tests for implemented functionality.

GC-16: Implemented issuance of client certificates:

- Added functional test covering basic issuance of client
certificates.
- Replaced the dummy command implementation.
- Added new crypto function that can be used for issuing TLS client
certificates.
- Implemented relevant unit tests.

GC-17: Refactored init command to handle output and return exit code:

- Introduced a holder class for command exit codes.
- Moved output for the cli module to commands module.
- Implemented new tests for verifying the command output.
- Updated existing tests for verifying return value of command output.
- Updated existing code and tests to use the new signature for init
command.

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-3: Implemented CA hierarchy initialisation:

- Added functional test for initialising hierarchy on a fresh
directory.
- Implemented the init command.
- Added two new modules for working with storage and crypto.
- Added cryptography (for certificate issuance and crypto) and
python-dateutil (for better handling of certificate validities) as
installation dependencies.
- Added freezegun as test dependency (helps with testing validity
dates).
- Implemented necessary unit tests.