Support for default values

I wanted the ability to supply default values like so:
````ruby
class MyPage
  include PageObject
  
  page_url "#{FigNewton.base_url("http://cheezyworld.com")}/my_page.html"
end
````

I also added support for more complex defaults supplied in blocks, Procs and lambdas...

The .rvmrc was creating a gemset for data_magic so I fixed that as well.