`compile` should allow DSDL compilation output to interleave with source DSDL files

```
yakut compile -o ~/.dsdl ~/.dsdl/uavcan
```

expected: generated python is interleved with the .dsdl files in this directory. This is a good way to keep both. side-by-side.

observed:
```
ValueError: The specified destination may overwrite the DSDL root namespace directory. Consider specifying a different output directory instead
```