Enhance documentation and examples to give the user a good overview of what is possible with VCTR

[JanosGit]

The root Readme should present the potential user a few more example use cases presenting

• The core types Vector/Array/Span
• Math expressions
• Convenience member functions

The examples folder should be populated with a few subfolders, each containing their own self-contained example project, showcasing functionalities for certain use-cases. Along with each project, there should be a Readme, explaining the features illustrated in the code example.

The generated doxygen output from the project should be reviewed and comments should be adjusted in order to generate the best possible documentation.