[FR] human readable name of benchmark

https://github.com/google/benchmark#running-a-subset-of-benchmarks
As shown in the readme.md,
https://github.com/google/benchmark/blame/master/README.md#L424

The benchmark name contains the state.range values as human readable format. (eg. `32k`)
But the current code does not provide any switches or automatic way to format these numbers to human readable format.
```
Benchmark Time CPU Iterations
----------------------------------------------------
BM_memcpy/32 11 ns 11 ns 79545455
BM_memcpy/32k 2181 ns 2185 ns 324074
```

**Describe the solution you'd like**
Provide a function to enable human readable names for benchmark names.
for powers of 2 and powers of 10.