Add minimal methods reflection capability to help when debugging.

I've added 'methods', 'leaf_methods', and 'wrapper_methods'.  These may not be of general interest, so you may not want to merge them into the main repository.  My motivation for writing them was to improve the integration of 'dumb_delegator' with various debuggers and DCI frameworks.  I've left identify alone, but enhanced the ability to know what methods are available at various levels of delegation.