Fixes RT#84863: Unindented text isn't code; needs to be ignored

This fixes RT#84863: https://rt.cpan.org/Ticket/Display.html?id=84863
A test testing this feature is also included.
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Fixed issue:

Say, we have this SYNOPSIS:

```perl
=head1 SYNOPSIS

Print some foos:

    print "Foos!\n";

And then print some bars:

   print "Bars\n";

=cut
```

Only the `print` statements will be rendered as code in the POD, but this module currently assumes the plain text portions are part of the code. This pull request fixes the issue.