Replace CLI parsing functionality with the `kingpin` library to better
support configuring the tool with environment variables.
Add new environment variables to configure the tool.
BREAKING CHANGE: CLI params now require two dashes instead of one (e.g. `--socket`)
Add support for connecting the exporter directly to the fail2ban server's
socket to send requests and receive data. The path to the socket file is
optional and specified on startup.
Export a new metric based on the response of the `ping` command sent to the
fail2ban server. The metric is set to 1 if the server responds with `pong`
and 0 in any other case. This metric is only shown if the path to the
socket file was provided on startup.
Update the project structure to move all golang files to a new `src/`
folder. This keeps all the code located in the same place and easier to
work with.
Update the Makefile and goreleaser config to continue to work with the new
folder structure.
