Segmentation Fault when Output-Dir doesn't exist

**Explanation**:
When the output directory doesn't exist, the program segmentation faults. I.e., it yet doesn't check if the output directory exists. 

**How to reproduce**:
_(OS: Linux)_

Compile the program, then run the program
```bash
./kongruent [...] -i <input_dir>/ -o <output_dir>/
```
If `output_dir` doesn't exist, the program segmentation faults during `export`