FTPS support 

With the help of the double-bag-ftps dependencie I developed the option to use FTPS explicite.
You just have to add the "ftp_secure: true" option in your _config.yml.

If it's not set it defaults to false so nothing changes, in the default settings standard ftp works as usual.

I added this functionality because I didn't want to send my plain password over the internet.
Unfortunately I have never before coded something in Ruby so I hope there are no newbie errors.
Also I'm not sure how to develop the tests in Ruby and we should probably add double-bag-ftps dependencie as an dependencie to the project.

If someone gives me some hints I will glady try to do this stuff.

Other than that I'm using the ftps functionlity right now and didn't encounter any problems yet.