#923 Create /authme purgeplayer command

- Create command to purge a specific player name
- Update docs

src/main/java/fr/xephi/authme/command/executable/authme/PurgePlayerCommand.java

@@ -0,0 +1,46 @@
+package fr.xephi.authme.command.executable.authme;
+
+import fr.xephi.authme.command.ExecutableCommand;
+import fr.xephi.authme.datasource.DataSource;
+import fr.xephi.authme.service.BukkitService;
+import fr.xephi.authme.task.purge.PurgeExecutor;
+import org.bukkit.OfflinePlayer;
+import org.bukkit.command.CommandSender;
+
+import javax.inject.Inject;
+import java.util.List;
+
+import static java.util.Collections.singletonList;
+
+/**
+ * Command to purge a player.
+ */
+public class PurgePlayerCommand implements ExecutableCommand {
+
+    @Inject
+    private PurgeExecutor purgeExecutor;
+
+    @Inject
+    private BukkitService bukkitService;
+
+    @Inject
+    private DataSource dataSource;
+
+    @Override
+    public void executeCommand(CommandSender sender, List<String> arguments) {
+        String option = arguments.size() > 1 ? arguments.get(1) : null;
+        bukkitService.runTaskOptionallyAsync(
+            () -> executeCommand(sender, arguments.get(0), option));
+    }
+
+    private void executeCommand(CommandSender sender, String name, String option) {
+        if ("force".equals(option) || !dataSource.isAuthAvailable(name)) {
+            OfflinePlayer offlinePlayer = bukkitService.getOfflinePlayer(name);
+            purgeExecutor.executePurge(singletonList(offlinePlayer), singletonList(name.toLowerCase()));
+            sender.sendMessage("Purged data for player " + name);
+        } else {
+            sender.sendMessage("This player is still registered! Are you sure you want to proceed? "
+                + "Use '/authme purgeplayer " + name + " force' to run the command anyway");
+        }
+    }
+}