Changed `-D` option to always download the lists supplied, regardless of
the database directory being empty or not.
This means you can download additional lists after the first program
run, or re-download lists later on. It *will* overwrite your custom
changes however if your files are called the same as the default list
names.
Additionally removed dependency on GNU version of cut and added some
simple tests for the download functionality.
Fixes #16.
Now that the project is finding a little adoption it is really high time
to bring some tests into the code to ensure everything works as it
should.
This first version will only provide a simple test harness from which
tests can slowly be written for other parts of the program.
