Allow Magento to be installed in a sub-directory

Hello, I am using Magentify in some projects and it is awesome. The problem I have is my Magento is not installed in the root folder of the project and the deploy process fails. Tweaking the settings in the deploy.rb file didn't make it work properly.

So I made a little improvement, I added a mage_base variable (that defaults to "" in case you don't define it, so older scripts continue working) that indicates the subdirectory where magento is installed.

I have no previous experience with Ruby, but I tested the deployment process with various projects and I had no problems.

If you do not consider this feature useful or necessary, please reject this pull request.

Thank you very much.
Javi.