feat: Maintainability and much more...

[carlocorradini]

Improving maintainability 🥳🤗🤯 The CHANGELOG.md file contains every relevant changes. The modifications are listed in the list below:

• All includes must be preceded by the word erkir: #include <erkir/FILE.h>
• Single include header file, erkir.h, exports all library's component
• Tests implemented with GoogleTest
• CI enhancements (you can push a tag and a new release is automatically created only if all checks pass)
• Overall code and repository structure have been reworked to improve maintainability

@vahancho I was also considering changing the extension of all header files from .h to .hpp because this is a "pure" C++ project rather than a C one (and also good practice 😊).

Please let me know what you think 🥳🤗🤯