Start implementation, but has compiler error.
Implement operator==(lhs, rhs).

Implement operator==(lhs, rhs) to make the code compile without errors.
Add files.
Merge branch 'master' into item02
Fixed CMakeLists.txt files.
Added item 3.
Added slicing from item 3.
Merge branch 'master' into item03
Finalize item 03.