Introduce scientific notation for counters in console

Sometimes it becomes difficult to grasp immediately the differences between benchmarked functions that have a wide variance in a given counter.
The aforementioned readability problem is due to the usage of the SI standard by default.
This one below is an example where I am dealing with different functions to approximate sine, look at the absolute error calculated for each one:
It's not instantly obvious how much more precise the first function is, but it would be using scientific notation:

The usage might be as easy as:
```cpp
state.counters["Foo"] = Counter(fooVal, benchmark::Counter::kScientificNotation);
```