Greatly improve Brigardier support

src/main/kotlin/net/axay/kspigot/commands/Requires.kt

@@ -0,0 +1,25 @@
+package net.axay.kspigot.commands
+
+import com.mojang.brigadier.builder.ArgumentBuilder
+import net.axay.kspigot.commands.internal.ServerCommandSource
+import org.bukkit.permissions.Permission
+
+/**
+ * Defines that the given [permission] is required to interact with this
+ * path of the command.
+ */
+fun ArgumentBuilder<ServerCommandSource, *>.requiresPermission(permission: String) {
+    requires {
+        it.bukkitSender.hasPermission(permission)
+    }
+}
+
+/**
+ * Defines that the given [permission] is required to interact with this
+ * path of the command.
+ */
+fun ArgumentBuilder<ServerCommandSource, *>.requiresPermission(permission: Permission) {
+    requires {
+        it.bukkitSender.hasPermission(permission)
+    }
+}