introduce BytesIO

rename secop.stringio to secop.io, which includes now
also BytesIO and the common base class IOBase

+ a small fix in error handling

Change-Id: I8e305e2c164f4ed131f4b36ef45edd8bd222336d
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/26393
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop_psi/ppms.py

@@ -43,7 +43,7 @@ from secop.lib.enum import Enum
 from secop.modules import Attached, Communicator, Done, \
     Drivable, Parameter, Property, Readable
 from secop.poller import Poller
-from secop.stringio import HasIodev
+from secop.io import HasIodev
 
 try:
     import secop_psi.ppmswindows as ppmshw