Parse regular /* comments as well as jsdoc-style /** comments

First, I wanted to thank you for this project. It's super useful!

I am wondering what the expected behavior should be if you send doctrine a regular `/*`-style comment instead of a jsdoc `/**`-style comment. Right now, what it does seems broken:

```javascript
doctrine.parse("/*\n* hello\n*/", {unwrap: true}); =>  { description: '/*\nhello', tags: [] }
```

This pull request makes regular block comments work like jsdoc comments:

```javascript
doctrine.parse("/*\n* hello\n*/", {unwrap: true}); =>  { description: 'hello', tags: [] }
```

Alternatively, perhaps it could throw an exception or something?