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).
Without this tern likes to return comments that start with an asterisk which also doesn't make sense. This fix applies to both fullDocs and the first sentence doc mode.

Example:

```javascript
/** test comments */
function test(){}
```

Without this fix *(current state of tern)* the resulting comment is `* test comments`. With the fix the result is `test comments`. I can't think of any reason why someone would ever want a starting asterisk.