Better handle spaces between string list entries
Add a loopback extension example
Improve parsing of the config files

This will also now recognize (and strip) quotation marks from around values.
Don't split config sections into separate blocks
Trace config file names being loaded
Look for alsoft.conf in the XDG_CONFIG_DIRS and XDG_CONFIG_HOME directories

This follows the XDG Base Directory Specification. The old files/locations are
still supported, but configs found in XDG_CONFIG_DIRS take precedence over
/etc/openal/alsoft.conf, and a config found in XDG_CONFIG_HOME takes precedence
over $HOME/.alsoftrc.