Fix reserved identifier violations

Some identifiers [do not fit](https://www.securecoding.cert.org/confluence/display/cplusplus/DCL32-CPP.+Do+not+declare+or+define+a+reserved+identifier "Do not use identifiers that are reserved for the compiler implementation.") to the expected naming convention for the programming languages "C" and "C++". They can be renamed.

The probability for name clashes can also be reduced especially for include guards by the addition of the project name and a kind of universally unique identifier.
Agree with @nefthy: renaming needs to be consistent, like `__smth` to `_smth`, for all the cases.