[#14] use standard (Aether) coords string for artifact regexs

 * using the groupId:artifactId:ext[:classifier]:version to
   specify artifact regexs.
 * as the classifier is optional it needs to be handled more
   carefully in the filters.
Merge pull request #17 from psiroky/14-artifact-regex-str

[#14] use standard (Aether) coords string for artifact regexs