Support hidden commands

- CommandRegistration now has a structure to define
  it beind hidden
- Modify relevant parts to filter out hidden commands
- Essentially command is hidden from all other than
  command execution
- Sample in e2e tests
- Fixes #416

spring-shell-standard-commands/src/main/java/org/springframework/shell/standard/commands/Help.java

@@ -21,11 +21,13 @@ import java.io.Reader;
 import java.io.UncheckedIOException;
 import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.Map;
 
 import org.jline.utils.AttributedString;
 
 import org.springframework.core.io.Resource;
+import org.springframework.shell.Utils;
 import org.springframework.shell.command.CommandRegistration;
 import org.springframework.shell.standard.AbstractShellComponent;
 import org.springframework.shell.standard.CommandValueProvider;
@@ -114,7 +116,8 @@ public class Help extends AbstractShellComponent {
 	}
 
 	private AttributedString renderCommands() {
-		Map<String, CommandRegistration> registrations = getCommandCatalog().getRegistrations();
+		Map<String, CommandRegistration> registrations = Utils
+				.removeHiddenCommands(getCommandCatalog().getRegistrations());
 
 		boolean isStg = this.commandTemplate.endsWith(".stg");
 
@@ -127,7 +130,8 @@ public class Help extends AbstractShellComponent {
 	}
 
 	private AttributedString renderCommand(String command) {
-		Map<String, CommandRegistration> registrations = getCommandCatalog().getRegistrations();
+		Map<String, CommandRegistration> registrations = Utils
+				.removeHiddenCommands(getCommandCatalog().getRegistrations());
 		CommandRegistration registration = registrations.get(command);
 		if (registration == null) {
 			throw new IllegalArgumentException("Unknown command '" + command + "'");