Patch for exception.h

[Friedrich W. H. Kossebau]

Hi Christian,

Am Mittwoch, 24. März 2021, 20:49:16 CET schrieb Christian Riggenbach:
> Hi Threadweaver team
> 
> I found a small error in the source code, which inhibits the inclusion of
> <Threadweaver/Exception> in my own program to throw an exception to fail a
> job: The include for threadweaver_export.h uses <> instead of "", which
> gives you a file- not-found error from the compiler.
> 
> Forgive me for posting a link to github, but it is a really small fix:
> https://github.com/eringerli/threadweaver/commit/
> f7e480e9bd9a3a6dd7f0bed67a4f853e2e339c95[1]

Thanks for the pointer. Forgiven, but then forgive me for being lazy as well 
and not setting up a remote to fetch your commit but doing a new commit myself 
directly :)

Interesting that you are the first one to hit this in all the years... but I 
agree with your fix, is consistent with the other export header includes and 
needed, both for the CamelCase forward includes but also the normal direct 
include <hreadweaver/exception.h> as well.

Cheers
Friedrich