Add Dockerfile

[jeinwag]

Since fabio is something that I'd probably like to see running in a container, I've added a Dockerfile.
Yields a small image (about 16 MB).
Inspired by Jeff Lindsay's Dockerfile for registrator.

[magiconair]

I'll try that myself first before I merge.

[magiconair]

I've produced an official image from a scratch container also with the integrated ca-certificates.crt file to provide proper SSL support but I still need to test that with a valid cert. Could you try whether this image works for you since I'm not using Docker? If it is OK then I'll push my change.

docker run -d -p 9999:9999 -p 9998:9998 -v $PWD/fabio.properties:/fabio.properties magiconair/fabio

[jeinwag]

Thanks, looks good to me!

[magiconair]

I've moved the config file from /fabio.properties to /etc/fabio/fabio.properties so that you can store the configuration and one or more SSL certs in a single directory and just mount that instead of the individual files. I've updated the magiconair/fabio:latest and magiconair/fabio:1.0.3 docker images accordingly.

Docker support is now official and I'm closing this pull request (not merging)