Add PERMS options to create temp file with given file permissions

[timgimyee]

Fixes #15.

[karenetheridge]

see reservations from the author at https://rt.cpan.org/Ticket/Display.html?id=82516

[timgimyee]

The author suggests that limiting to only overridden temp directories might be okay. So check for DIR option and that it isn't the default temp directory.

The PERMS option could also warn when used.

Any other ideas to keep the temp files safe? Or at least safer than the chmod work-around:

my ($fh, $tempfile) = tempfile();
chmod 0666, $tempfile or die $!;

[mohawk2]

@xdg Would timgimyee's point be acceptable to you?

[xdg]

No strong feelings. If users want control over PERMS, that seems fine with me, with or without DIR.