Add support for collecting arbitrary metrics from a textfile as well as
metrics collected from fail2ban. This allows other data to be exported
along with the fail2ban metrics (e.g. instance metadata).
Update the docker image to allow mounting a folder with a collection of
metric files to be exported. Only files ending in `.prom` with be read.
Update project README with the new functionality.
Update the docker container to support mounting the fail2ban server socket
and pointing the exporter at it. This allows the exporter to interact with
the socket from within the container.
The entire `/var/run` folder is mounted instead of just the socket file to
correctly handle fail2ban restarts (where the file will be deleted).
Add a project Dockerfile to allow deploying the application in a docker
container. Add a `run.sh` script to start the application in the container.
Add Makefile commands to build the docker image based on the Dockerfile.
Fix possible nil reference error in the `db` package.
