Respect configuration in $HOME/etc/wemux.conf

[traumschule]

This commit changes wemux to also read configuration from the home directory for when users have no write access to /usr/local/etc/.

In the future it might be useful to add an option (e.g. -c) to let users define other locations.

[Rondom]

I think $HOME/etc is pretty non-standard.
What tmux does, sounds sane:

By default, tmux loads the system configuration file from /etc/tmux.conf, if present, then looks for a user configuration file at ~/.tmux.conf, $XDG_CONFIG_HOME/tmux/tmux.conf or ~/.config/tmux/tmux.conf.