Add json export of mmdb metadata

[jhg03a]

I'd like to see a new -meta CLI arg to simply print the mmdb metadata on disk. This allows for greater control over consuming services by leveraging the built in timestamp of the mmdb rather than dealing with exit codes or file mtime. While my current example really only cares about one field from the metadata, it is conceivable other pieces might be relevant to someone. Additionally it's trivial to use tools like ansible or jq to extract the one piece of data from the json I care about. If there's enough support though just having a -publishedTime or something along those lines just for the timestamp could simplify things for others. This would fall in line with similar asks for better control mechanisms like #25.

[jhg03a]

It is possible to do things this way as it is by using a separate mmdb reader application, but I think this is a small enough ask for a big gain.

[oschwald]

I don't think we are likely to do this. It seems somewhat orthogonal to what this package does. It currently doesn't import a database reader and cannot read the metadata from the files. I think it would be best to use a separate tool for this.