Add --classifier option

cli/src/main/scala-2.11/coursier/cli/Coursier.scala

@@ -50,6 +50,10 @@ case class CommonOptions(
     exclude: List[String],
   @Help("Consider provided dependencies to be intransitive. Applies to all the provided dependencies.")
     intransitive: Boolean,
+  @Help("Classifiers that should be fetched")
+  @Value("classifier1,classifier2,...")
+  @Short("C")
+    classifier: List[String],
   @Help("Maximum number of parallel downloads (default: 6)")
   @Short("n")
     parallel: Int = 6,
@@ -60,6 +64,7 @@ case class CommonOptions(
     cacheOptions: CacheOptions
 ) {
   val verbose0 = verbose.length - (if (quiet) 1 else 0)
+  lazy val classifier0 = classifier.flatMap(_.split(',')).filter(_.nonEmpty)
 }
 
 case class CacheOptions(

cli/src/main/scala-2.11/coursier/cli/Helper.scala

@@ -288,14 +288,14 @@ class Helper(
     val res0 = Option(subset).fold(res)(res.subset)
 
     val artifacts =
-      if (sources || javadoc) {
-        var classifiers = Seq.empty[String]
+      if (classifier0.nonEmpty || sources || javadoc) {
+        var classifiers = classifier0
         if (sources)
           classifiers = classifiers :+ "sources"
         if (javadoc)
           classifiers = classifiers :+ "javadoc"
 
-        res0.classifiersArtifacts(classifiers)
+        res0.classifiersArtifacts(classifiers.distinct)
       } else
         res0.artifacts