'git mv' rst resources to md

This is mainly intended to keep the git history as neat as possible.
No actual conversion yet, so now both the rst and the paradox docs
are broken, which will be fixed in the next commits.

akka-docs/src/main/paradox/java/code/jdocs/stream/SilenceSystemOut.java

@@ -0,0 +1,64 @@
+package jdocs.stream;
+
+import akka.actor.ActorRef;
+
+import java.util.function.Predicate;
+
+/**
+ * Acts as if `System.out.println()` yet swallows all messages. Useful for putting printlines in examples yet without poluting the build with them.
+ */
+public class SilenceSystemOut {
+
+  private SilenceSystemOut() {
+  }
+
+  public static System get() {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        // ignore
+      }
+    });
+  }
+
+  public static System get(ActorRef probe) {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        probe.tell(s, ActorRef.noSender());
+      }
+    });
+  }
+
+  public static System get(Predicate<String> filter, ActorRef probe) {
+    return new System(new System.Println() {
+      @Override
+      public void println(String s) {
+        if (filter.test(s))
+          probe.tell(s, ActorRef.noSender());
+      }
+    });
+  }
+
+  public static class System {
+    public final Println out;
+
+    public System(Println out) {
+      this.out = out;
+    }
+
+    public static abstract class Println {
+      public abstract void println(String s);
+
+      public void println(Object s) {
+        println(s.toString());
+      }
+
+      public void printf(String format, Object... args) {
+        println(String.format(format, args));
+      }
+    }
+
+  }
+
+}