Fixed about_class_methods.rb to pass tests

Learned that:
* objects are objects and classes are classes,
* classes are objects too,
* objects and classes have methods.

[#65851794]
Fixed about_class_methods.rb to pass tests

Learned that:
* you can define methods on individual objects,
* and other objects are not affected by these singleton methods,
* classes and instances do not share instance variables,
* you can define class methods inside the class.

[#65851794]
Fixed about_class_methods.rb to pass tests

Learned that:
* class statements return the value of their last expression,
* self while inside class is class object not instance,
* you can use self instead of an explicit reference,
* there's more than one way to write class methods.

[#65851794]
Merge pull request #26 from mkreyman/65851794_about_class_methods_master

about class methods master

[Delivers #65851794]