Emails with returns that split text fail seeInEmail assertions

When you have an email with content which has text that is cut off onto a new line, for example:

```
This is the te=\r\n
xt that I am searching for.
```

If you assert that you see `This is the text that I am searching for` then it will fail due to where the return is.

We should be using PHP's `quoted_printable_decode` but bear in mind that for URL detection this cannot be used (#63)