Make the cycle more precise

Measure each cycle of process image synchronisation and do not build a mean value for that.
The cycle function is now exactly timed, even if the individual runtimes are different.

setup.py

@@ -17,7 +17,7 @@ setup(
 
     license="LGPLv3",
     name="revpimodio2",
-    version="2.5.8",
+    version="2.5.8b",
 
     packages=["revpimodio2"],
     python_requires="~=3.2",