'tor --dump-config' without an opt should provide usage information
From legacy/trac#14742, 'tor --dump-config' should provide usage information when no arguments are provided. Presently I guess it's just a no-op which is confusing.
```
atagar@odin:~/Desktop/stem$ tor --dump-config
atagar@odin:~/Desktop/stem$ tor --dump-config short
DataDirectory /home/atagar/.tor
```
issue