Support for "-f -"

Hi! 

First of all - thanks for creating this project - since `jsctags/doctorjs` has been abandoned I was looking for something like that, especially that excuberant-ctag's Javascript support isn't getting any better.

Now, for the pull request itself:

All ctags compatible tools I've used so far (or [wrote myself](https://github.com/lukaszkorecki/coffeetags) need to support `-` as a tags file option which by convention means "print to stdout".

That makes `javascript-ctags` work with such tools as [tagbar plugin] for Vim (and similar plugins/tools for other editors).

Here's a screenshot: 
![tagbar + javascript-ctags](https://dl.dropboxusercontent.com/u/29110/screens/javascript-ctags.png)

To make this work with vim a bit of configuration is needed, stored in `~/.vim/ftplugin/javascript/tagbar-javascript.vim`:

```viml

let g:tagbar_type_javascript = {
      \ 'ctagsbin' : 'javascript-ctags',
      \ 'ctagstype' : 'javascript',
      \ 'sro' : '.',
      \ 'kinds' : [
        \ 'f:functions:1'
      \ ],
      \'kind2scope ' : {  'f' : 'function' },
      \'scope2kind' : {  'function' : 'f' }
    \}
```

I believe that this also makes `javascript-ctags` work with Sublime Text's ctags plugin as well, although I don't use it myself.