Automate release to Maven Central

[filfreire]

Looking at #36 it seems that a release to Maven Central of scalatest-maven-plugin is not automated and readily available to contributors via a script/command.

I have a suggestion to automate release process, we could use a Devops bot like Rultor and define the release routine in a script.

That way, certain contributors with the permissions defined on a Yaml file can easily comment on a issue or PR in this repository telling the bot to release to maven central with a given version.
It can then be defined that the bot runs a battery of tests, tags a release for github and releases to maven central.

FYI @cheeseng @bvenners

[filfreire]

@gcberger FYI