Process stdout should not use CharStream.copy

**Describe the bug**
`setProcessOutputStream` takes in an Appendable, and later uses CharStreams.copy to transfer the output as text.
This does not work for most cases, as stdout is used to write the output streams.
This means, an encoded file would be interpreted as chars, causing some bytes being lost due to interpretation.

**To Reproduce**
```java
// appendable should be a handle to a file

FFmpeg ffmpeg = new FFmpeg();
ffmpeg.setProcessOutputStream(appenable);

ffmpeg.run(new FFmpegBuilder().addInput("input.mp4")).done().addStdoutOutput().done().build());
```

**Expected behavior**
processOutputStream should be treated as binary.

**Version (if applicable):**
- OS: any
- Java Version: any
- FFmpeg version: any