- add unregister_callback (this is needed for the SECoP client in nicos) - improve error handling - imporve error handling in AsynTcp - also improve error handling on StringIO Change-Id: If4f3632a93cbc0e7fbc55a966e09fcc3e69c09b7 Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22852 Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de> Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de> Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>