Overwritten values

[michip]

When a key is already present in a measurement and is overwritten by aemeasure, it would be great to get some warning. I had the issue when measuring my own runtime in microseconds and saving with the key 'runtime' key.

[d-krupke]

The new library AlgBench does separate automatic and user values better (and is probably better in general). Don't know if I will invest time to fix this library.