Feature: tunnelFlags option added

Hi,
Here is a pull request that allows to pass tunnel option flags through grunt ``tunnelFlags`` option.

I also:
* removed ``tunnelTimeout`` as it is no longer supported by latest sauce-tunnel package,
* updated npm packages listed in package.json
* updated the README.md (I also added hostname and port option description that I forgot to add in my previous pull request)

Thanks,

Saad