Added pom.xml to distribute the CSL styles via Maven

Hi folks!

I'm currently working on a project called 'citeproc-java' which is a small wrapper around citeproc-js with some additional stuff (such as bibtex conversion). The GitHub repo will be published soon. I will announce this on the mailing list, probably later today.

Since I would like to publish citeproc-java via Maven it makes sense to also publish the styles there so they are directly available for Java applications. That's why I'm sending you this pull request.

Please have a look at the version number. Currently I chose 1.0.2-SNAPSHOT. You should verify that this is OK.

Apart from that, I put myself in the developer's section so I can upload the artifact to Maven central with my user id michel-kraemer. If you have your own user id for Maven central you may of course replace my name and id with yours. If not, I would kindly ask you to allow me to create the `org.citationstyles` group id on Maven Central on your behalf. Of course, we can add more developers/contributors to the pom file if necessary.

Cheers,
Michel