def filter(name, callable=nil, &block)
      if block_given?
        transforms[name.to_sym] = block
      else
        transforms[name.to_sym] = callable
      end
    end
def filter(name, callable=nil, &block)
      if block_given?
        transforms[name.to_sym] = block
      else
        transforms[name.to_sym] = callable
      end
    end
Registers the given block as a string filter.

 @param [Symbol] name
 @yield [String]
 @yieldreturn [String]