Change command usage

Per conversation with @ezimuel on IRC, changed command usage to:

```console
$ zfdeploy.php <package filename> [options]
```

The `-t|--target` option is now optional, and will use the value of
`getcwd()` if not provided.
Fixed handling of app path validation

- `@require` led to silent failures. Modified to do both a `file_exists`
  and `include` on the file.
- Moved all fileOut validations together.