Remove not needed abstract classes

The constructor classes are not needed for making the library work.
So I removed them.

lib/rubella/input/base.rb

@@ -1,42 +1,14 @@
 module Rubella
   module Input
 
-    # Gets the rwa data and translate it into a by the Rubella::Weighting::Base
-    # class readable format.
+    # Gets the raw data and translate it into a readable format for the
+    # Rubella::Weighting::Base class.
     # This must be an array within subarrays, which have all the same lenght
     # and contains only numeric data.
     #
-    # TODO The validation of the data should happen here
-    # Check if data is array, with subarrays. Check, that all sub array have
-    # the same size. Check that all the content are numeric values between 0
-    # and 100.
-    #
     class Base
       attr_reader :data
 
-      # Constructor
-      # Creates a new Rubella::Input::Base object, from the given data.
-      #
-      # @param value string A string, which contains the data
-      # @return Rubella::Input::Base
-      #
-      def self.string value
-        raise NotImplementedError.new "Please override 'self.string' in your "+
-          "concrete implementation"
-      end
-
-      # Constructor
-      # Creates a new Rubella::Input::Base object, from the given file.
-      # Only the file name is required.
-      #
-      # @param file_name string The name of the file
-      # @return Rubella:Input::Base
-      #
-      def self.file file_name
-        raise NotImplementedError.new "Please override 'self.file' in your "+
-          "concrete implementation"
-      end
-
       # Passes each dataset trought the given block.
       #
       # @param pointer to block