Breaking: Rewrite config (INI) library to provide an associative array

[DannyBen]

As discussed in #405

---

This PR updates the config library with these changes:

1. config_load FILENAME will set an associative array named config with all the values.
2. Added support for INI sections which will be presented with dot notation in the associative array (section.key).
3. config_show will show the loaded config key/value pairs.
4. config_save FILENAME will save the filename.
5. All other config methods were removed.