Slurp all of perl files if script executes with no file args

e.g.
```
$ prt replace_token foo bar
```

Slurp all of perl files that are in project (definition of project root: path that contains cpanfile or .git)
Now this script ignores files that are in the following directories;

- share/
- fatlib/
- _build/
- .git/
- blib/
- local/

Are these enough? How do you feel?