Adjust documentation of first three chapters to the corresponding sources.

[asuessenbach]

The adjustments in 02_validation_layers.adoc required some changes in 02_validation_layers.cpp.

As usual, if those changes are considered to be ok, I can carry them over to all the other chapters.

[asuessenbach]

Any opinions?

[SaschaWillems]

Can you elaborate a bit? This looks like a pretty substantial change.

[asuessenbach]

Can you elaborate a bit? This looks like a pretty substantial change.

Essentially, I replaced all occurances of C-style vulkan terminology to C++-style in 00_Base_code.adoc, 01_Instance.adoc, and 02_Validation_layers.adoc.
While doing that, I adjusted the documentation to the actual code in the corresponding code files 00_base_code.cpp, 01_instance_creation.cpp, and 02_validation_layers.cpp.
While doing that, I realized that parts of the documentation in 02_Validation_layers.adoc where "better" than the documented code, so I adjusted those parts in 02_validation_layers.cpp accordingly.

If there are any parts in this PR that needs more explanation, please let me know.