To prevent having users always specify the configuration file, the path
now defaults to $XDG_CONFIG_HOME/neosay/config.json. This way it is
possible to send messages from a "default identity" like this:
echo "look mom, I'm in someone's commit history!" | neosay
To make the code more succinct, flag parsing is no longer done manually,
but instead using the flag package from stdlib.
Fixes: https://github.com/donuts-are-good/neosay/issues/2
Signed-off-by: Moritz Poldrack <git@moritz.sh>
