Provide the core detect logic as a separate artifact

[tisonkun]

It's a bit common to use the resolved classifier in code in addition to in pom.xml. Although we may use a filtered resource file, it resolved the classfier at compile time instead of runtime.

Of course I can refactor out the related code from this project, but I wonder if it can be done in the upstream so that we're sure the same logic is used between the plugin and library.

cc @trustin I can invest some time to work on an implementation, but it can change the structure of this project so I'd like to ask for a consensus first.