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/modules.py

@@ -410,7 +410,7 @@ class Module(HasAccessibles):
             for pname, p in self.parameters.items():
                 try:
                     p.checkProperties()
-                except ConfigError:
+                except ConfigError as e:
                     errors.append('%s: %s' % (pname, e))
         if errors:
             raise ConfigError(errors)