allow per-user suppression of clinte notifications
If a user places a file at $HOME/.hushclinte, they will not be
notified of new posts on login.
Moved check logic to a function. Test if .hushclinte exists. If
it doesn't, run the announce function (check_clinte).
Also fixed a shellcheck error - unquoted variable expansion.
Changed string literals to single-quotes.
testing for OS to improve portability of new post notification
added extra newline after new message notification
redirecting stderr to /dev/null
stops an error if a user has never used clinte
moved hashing to shellscript to check for posts
removes dependency on sha2 crate and allows users
to choose their own hashing algorithm easily.
now copies clinte.json to $HOME/.clinte.json once
the posts are viewed. a shellscript can be used to
compare the hash of the global clinte.json to the
hash of the copy. an example script is supplied.
on `make install` the example script is installed
to /etc/profile.d/, where it will be run for users