f3write speed graph

Hello!

Modern SSD has different speeds depend on data written. For small amounts (few GB) write speed can be 400MB/s, the rest of flash writing at 40MB/s speed. This is normal. But f3write tool only reporting average speed.

This should be addressed and average speed replaced with speed graph. Lets say current output:

```
Creating file 235.h2w ... OK!
Creating file 236.h2w ... OK!
Creating file 237.h2w ... OK!
Free space: 0.00 Byte
Average writing speed: 60.20 MB/s
```

Expected output:

```
Creating file 235.h2w ... OK!
Creating file 236.h2w ... OK!
Creating file 237.h2w ... OK!
Free space: 0.00 Byte
10% 400MB/s
20% 400MB/s
30% 30MB/s
...
90% 30MB/s
100% 30MB/s
Average writing speed: 60.20 MB/s
```

it could be smart and detect speed drops measuring exact GB speed get lower significantly:

Expected output:

```
Creating file 235.h2w ... OK!
Creating file 236.h2w ... OK!
Creating file 237.h2w ... OK!
Free space: 0.00 Byte
0-1% 400MB/s
1-100% 30MB/s
Average writing speed: 60.20 MB/s
```