Add !mute & !silent

[PoorlyDefinedBehaviour]

Add two comands: !mute & !silent Add arg to context object, which can be used instead of args[0] when the command takes only one argument

Example:

• Before

  public async run({args}: Context): Promise<void> {
  foo(args[0])
  ...
  }

• Now

  public async run({arg}: Context): Promise<void> {
  foo(arg)
  ...
  }

args can still be used when the command takes more than one argument(more than one word separated by spaces)