Closes #19

This reduces the size of the code from 208608 to 208072 bytes, which is
totally negligible

Update documentation for the ECSS definitions

Group Services and ECSS Definitions into a doxygen page

Use a non-templated version of etl::string

Set the etl format as a static variable for the Logger

This prevents wasting time recreating the format variable every time the
LOG function is called.

Force inlining the LOG function

This forces the compiler to check the `if constexpr` structure, and
disable the logging line entirely if needed.

Never redefine the log level

Move `disabled` logging level to ease level checks

Take care of MISRA and vera++ concerns