Implemented Kernel#respond_to_missing? (almost)

Not implemented only case with private method

 * Kernel#respond_to_missing? is called with a 2nd argument of
   false when #respond_to? is
 * Kernel#respond_to_missing? is called a 2nd argument of false
   when #respond_to? is called with
 * Kernel#respond_to_missing? is called with true as the second
   argument when #respond_to? is
 * Kernel#respond_to_missing? is called when #respond_to? would return false
 * Kernel#respond_to_missing? causes #respond_to? to return true
   if called and not returning fal
 * Kernel#respond_to_missing? causes #respond_to? to return false if called
   and returning false
 * Kernel#respond_to_missing? causes #respond_to? to return false if called
   and returning nil
 * Kernel#respond_to_missing? is called for missing class methods
 * Kernel#respond_to_missing? returns true if obj responds to the given
   public method
Simplified code a little bit
Merge pull request #541 from krekoten/kernel_respond_to_missing

Implemented Kernel#respond_to_missing? (almost)