Allow plain Arrays and Vectors to be used as arguments

openscad allows code without parameter names like this ```translate([-10,0,0]) cube([10,20,10]);```, because typing them all the time is annoying.

This commit makes the same thing possible in RubyScad, so that ```translate([-10,0,0])``` and ``` cube([10,20,10])``` just work as expected.

Furthermore also the Readme was updated to document the new behavior.

I hope I implemented the change not too hacky, feel free to tell me how to do it better. I'd be happy to update this pull requests if there are any problems/nits.