Injection vulnerability in ExIRC.Client.msg() / IRC standard nonconformance

I'll present this as a little story:

Suppose we are implementing a bot that reads the titles from Web pages and posts them on IRC, a classic.

As a short introduction (only vaguely related to the bug), further suppose that we are using Floki (which is also [not standards conformant](https://github.com/philss/floki/issues/421)) to parse the title of say, this webpage:
```html

I don't want to
quit programming!
…
```
(this is conformant HTML, even though the formatting isn't pretty!)

Assume the result gets into `title = "I don't want to\nquit programming!"`… and we get to the ExIRC bug:

```elixir
ExIRC.Client.msg(state.client, :privmsg, dest, "Title: #{title}")
```

In the IRC channel we see:
```chat
https://domain.tld/blog/i-dont-want-to-quit-programming
Title: I don't want to
*potionbot has quit ("programming!")
```

Oops.

**Obvious solutions**:
- Panicking: cut off all text after the first newline to prevent the injection.
- Vengeful: throw an error if there is a newline in the message (this is not legal in the IRC standard anyway).
- Posed: make the type of the fourth argument of `ExIRC.Client.msg()` a `StringWithoutNewlines` type, preventing the error at compile time.
- Creative: post several messages in IRC, one per line.

My preference goes to the last two, and specifically both of them at once:
- Make `ExIRC.Client.msg()` refuse newlines, preventing the application from starting if that's not guarded against, and
- Introduce a new `ExIRC.Client.msg_multiline()` method that posts several messages to accomodate for the line feeds.

For more ideas, see https://eiv.dev