Reads a user-specified configuration file,
located in a "config.yml" file in the working directory.
If this file is not found, reads a default package configuration file.
By default, the sits configuration file "config.yml" is located at
the directory "extdata" of the package.
Users can provide additional configuration files, by specifying the
location of their file in the environmental variable
SITS_USER_CONFIG_FILE
To see the contents of the configuration file,
please use sits_config_show
.