Issue: GREG-36

Omits the test folder since checking coverage of the test functions
themselves makes little sense.

Pytest understands unittest-styled tests, so there is no immediate
need to update the test files themselves to a pytest idiomatic
syntax.

Fixes: GREG-14

Pylint analyses the code for common bugs.

Fixes: GREG-16

"make fmt" can now be invoked to auto-format Python code.

Fixes: GREG-16

Use black to check if the code is well-formatted and fail if it is not.

Fixes: GREG-16

Introduce a new lint task invoked through "make lint".  It currently
only lints the Poetry configuration.

The lint task is ran as part of the continuous integration pipeline.

Fixes: GREG-16

A Makefile's default target is either the one defined by "all", or in
the absence of an "all" target, the first target found in the file.

This means the current default target is to clean the venv from disk.
This patch makes calling make non-destructive by redefining the default
target to run the tests.

We may want to change this in future to something more appropriate.

Fixes: GREG-13

Fixes: GREG-13

Fixes: GREG-12

We have a bootstrapping problem on most operating systems because
the Poetry build system is not available as a distribution package.
This is a problem for some users because it hinders developer
productivity and automation.

This introduces a Makefile wrapper that installs Poetry into a venv
(under ./venv/ by default, or configurable with the VENV environment
variable).  Various tasks can be added to this Makefile so one can
easily interact with the build system without first having to
activate the venv.  This is useful for development environments
where you do not have access to an interactive terminal.

It is important to note that the Makefile is not actually a dependent
in the build process.  Using "poetry build", or any compatible
Python build system, should still work.  The Makefile is, then,
merely a set of shorthand helpers to make development somewhat more
enjoyable.

Fixes: GREG-12