fullDocs option for doc_comment

See [discussion](https://github.com/marijnh/tern/issues/411) about this.

Updated demo with default value for fullDocs to make it easy for users
to understand. Added documentation to manual.txt (I don't know how to run the Makefile to regenerate the manual.html file - I'm using Windows).
This removes all asterisks that are part of the JSDoc structure except the first one (which is removed later). This is important as it keeps asterisks that are part of the documentation; [example](http://usejsdoc.org/tags-example.html) of asterisk in documentation:
```
 /**
  * Solves equations of the form a * x = b
  */
```

This also preserves the newlines inside of the comments.