the wagn/decko asset pipeline (first step)

### introduces Machine and MachineInput cards

Machine and MachineInput are modules intended to be included in card sets.

a machine card 
- collects all items cards of all levels in a  pointer card +*machine input  (if the machine card is not a pointer the input card contains just the machine card itself)
- creates a file with the content of all input cards (if a input card is a machine input card the method machine_input is used to get its content otherwise the raw view)
- saves the file in a file card +*machine output 

a machine input card 
- provides input especially formatted for machine cards (e.g. a scss card provides compressed css)
- when changed it runs all machines that uses this input card, i.e. it updates the corresponding "+*machine output" files

Example from scss.rb (which is both machine and manchine input card):

    include Machine
    include MachineInput

    store_machine_output :filetype => "css"

    machine_input do 
       compressed_css format._render_raw
    end


TODO: fix old style migrations (they use machine input and output cards before they are defined)