``` should be stripped instead of triggering the "long message" mechanism

[progval]

Is your feature request related to a problem? Please describe.

When sending this on Matrix:

```
a
b
```

Matrix sends a huge pastebin link, such as:

* pinkie[m] < https://matrix.org/_matrix/media/r0/download/matrix.org/ZBiUWxhBCkRMCFIIXsfEYyTP/message.txt >

Describe the solution you'd like

Strip the backticks and send this instead:

<pinkie> a
<pinkie> b

And when a Matrix user sends

```
a
```

the bridge should not send this:

15:28 <pinkie[m]> ```
15:28 <pinkie[m]> a
15:28 <pinkie[m]> ```

but this:

15:28 <pinkie[m]> a

Because lines with the three backticks are just noise for IRC users, no client interprets Markdown (especially across lines) as far as I know. EDIT: actually IRCCloud does parse the backticks

However, the bridge could prefix such messages with the 0x11 byte, which indicates clients should format it with a monospace font.

Additional context
This happens to me frequently with people sharing short snippets.