Stow should look in $STOW_DIR for .stowrc

I was a bit surprised to realize that running stow from somewhere outside of my $STOW_DIR did not respect the .stowrc in $STOW_DIR. The documentation does indicate that this is expected behavior:

Stow searches for default command line options at .stowrc (current directory) and ~/.stowrc (home directory) in that order.

I feel that $STOW_DIR should be added to this list, since my understanding the point of $STOW_DIR is to let you run stow from outside of your $STOW_DIR. Of course, you can use the ~/.stowrc location (which I will start doing), but IMO the natural place to place your .stowrc is in your $STOW_DIR since it's likely version-controlled.

(Bonus suggestion: Look in ${XDG_CONFIG_HOME:-$HOME} instead of $HOME for .stowrc)