Patterns overhaul

Closes #8, #13, #14, and #17

See merge request Patterns!47

- Fix documentation in Error.
- Fix namespace of StateMachine.

- replace Patterns namespace with Pattern for design patterns,
- replace other Patterns occurrences with Essential.

As the whole library is going to be called Essential, port must be
called accordingly.

Usability/replace const char

See merge request Patterns!48

Now, module and class names are printed correctly.

Changes were made so the std:string_view variables are used properly
and the tests are able to compile.

Error module didn't work after replacing const char with std::string_view
so there were smaller altercations made in order to assure the the project
compiles.

Fix double dot in the error message

See merge request Patterns!46

Usability/error code print

See merge request Patterns!45

Add new error code CoprocessorResponse

See merge request Patterns!44

Refactor folder structure to the coding standard and tidier docs

See merge request aconnoProducts/aconnoLibs/Patterns!40

[[nodiscard]] was added to the Error::Case enumerator.

Introduced with C++17, the [[nodiscard]] attribute causes compiler to warn
if a function/value marked as nondiscard is unused.

Adding nodiscard attrbute to aconno Error::Code enum causes our entire codebase to
be covered with this - if Error::Code return value is ignored, warning will occur.

In some instances developer might really want to ignore a return value on purpose.
For this purpose DISCARD_RETURN() macro is provided.

Rename GPIO class to Pin.

This was done to match the folder structure.