Objectives:
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Meetup 1: class, module, instance variables, attribute accessors
notes: class includes module; the instance variables of the class
are visible by the module methods.
Meetup 2: class inheritance, module included, module not included.
notes:
a) we show 2 different ways to initialize instance variables, with "@name"
(see file person1.rb) and with "self.name" using the accessor methods
(see file person2.rb)
b) we have logic, in file user_of_person2.rb, of the class Person2 defined
in its own separate file; this is done using 'require'.