Check for .togglrc file in default XDG_CONFIG_HOME if env variable is unset

[swantzter]

Right now, .togglrc is only searched after in XDG_CONFIG_HOME if that environment variable is set, but according to the spec a default of $HOME/.config should be used if that environment variable is unset.

I can respect not wanting to write the file to ~/.config if it's not in use on that system, but I would prefer the following:

1. if XDG_CONFIG_HOME is set and $XDG_CONFIG_HOME/.togglrc exists - read and write to this file
2. if XDG_CONFIG_HOME is not set and $HOME/.config/.togglrc exists - read and write to this file
3. if XDG_CONFIG_HOME is not set and $HOME/.config/.togglrc does not exist exists - read and write from ~/.togglrc

When determening how to create the config file for the first time I'd recommend:

1. if XDG_CONFIG_HOME is set - create $XDG_CONFIG_HOME/.togglrc
2. if XDG_CONFIG_HOME is not set and $HOME/.config exists - create $HOME/.config/.togglrc
3. if XDG_CONFIG_HOME is not set and $HOME/.config/ does not exist exists - create $HOME/.togglrc