cheat sheets.

method_lister:
  used to query objects and discover which ancestor implements which methods.
    
  Methods:
  
  .ls([only_public]), .mls
    lists all methods an object responds to, organized by the module or class
    which provides the implementation.
    
  .grep(pattern, [only_public]), .mgrep
    takes a regular expression and only returns methods which match the given
    regex.
  
  .which(method_name)
     is for finding which classes or modules implement the method you're
     seeking. You can pass the method name in as a string or symbol.

     >> [].which :to_a
     ========== Module Kernel ==========
     PUBLIC: to_a

     ========== Module Enumerable ==========
     PUBLIC: to_a

     ========== Class Array ==========
     PUBLIC: to_a