Support a custom location for the config

Export $JRNL_CONFIG to override the location instead of using $HOME. Too many dotfiles are literring it, ya' know?

Linux desktop users, you might like if you follow the XDG standards:

    export JRNL_CONFIG=$XDG_CONFIG_HOME/jrnl/config
Merge branch 'patch-1' of git://github.com/evaryont/jrnl into evaryont-patch-1
Updated readme and changelog and changed config path according to discussion