Alternative subtype not properly handled about fetch

[tedivm]

I added some additional testing code over the last week, so you should try things again.

From the project root run "./tests/runTests.sh" rather than calling phpunit direct :-)

[dfreudenberger]

Hi @tedivm,

i just stumbled over an issue when dealing with inline attachments. The part containing the inline attachment has type 1 and subtype = related, which executes following branch https://github.com/tedious/Fetch/blob/master/src/Fetch/Message.php#L487

I tried to gather some information if that should be considered as expected behaviour. What do you think? In my opinion, getting the message body as plain text should not contain anything but human readable text.

If you agree I'd fix the issue and open a pr

[tedivm]

@dfreudenberger, I'd love it if you wanted to take a look at this.