Use the spdlog library for project wide logging to a file. Path of
logfile is configurable as command line option.

Change log:
* use spdlog
* set global logging to file
* logfile as command line option
* update README command line option section with logfile option
* update README command line option section with default values for options
* control log level with CMake build type variable
* log received request
* get request logging
* put request logging
* getmd request logging
* fifo logging
* rename authorisation macro to comply with linter
* use rotating files with size limit