whisper : add version function (#3289)

whisper : add version function (#3289)

* whisper : add version function

This commit adds a version function to the whisper API.

The motivation for this is that it might be convenient to have a way to
programmatically check the version.

Example usage:
```c++
printf("Using whisper version: %s\n", whisper_version());
```
Will output:
```console
Using whisper version: 1.7.6
```

* examples : add version to android example CMakeLists.txt