command-processing section.
Added new class server/config_ini.pp to manage contents of the config.ini.
Three new parameters added:
* command_threads
* store_usage
* temp_usage
All three default to 'undef'. This makes sure (potential) custom settings
done to that file with regard to above three variables are 'absent',
and let PuppetDB built-in defaults take care.
Documentation to the README.md added, as well as unit tests.
My use-case was, that I have on some nodes a too small /var partition,
so I had to lower the values of store-usage and temp-usage in the config.ini
manually.
