Modified C++ chapter

Added a section on modules. Added a subsection on return statements.
Modified statements section in C++ code generation.

Reference to a table was removed since it makes more sense to have separate sub sections for all statements.
There are only a few statements and each of them would require an example.
Added sub sections inside statement section

Each subsection will talk about a specific statement. Currently empty.
Modified assignment statements

completed sub sections on simple assignment statements and slice set assignment statements.
Modified assignment statement section.

Removed unnecessary indentations.