Implement channels.getMessages

[aykutalparslan]

Get channel/supergroup messages

messages.messages#8c718e87 messages:Vector<Message> chats:Vector<Chat> users:Vector<User> = messages.Messages; messages.messagesSlice#3a54685e flags:# inexact:flags.1?true count:int next_rate:flags.0?int offset_id_offset:flags.2?int messages:Vector<Message> chats:Vector<Chat> users:Vector<User> = messages.Messages; messages.channelMessages#64479808 flags:# inexact:flags.1?true pts:int count:int offset_id_offset:flags.2?int messages:Vector<Message> chats:Vector<Chat> users:Vector<User> = messages.Messages; messages.messagesNotModified#74535f21 count:int = messages.Messages; ---functions--- channels.getMessages#ad8c9a23 channel:InputChannel id:Vector<InputMessage> = messages.Messages;