my encrypted messaging protocol

to run this, just run

     cargo run --bin client sugar

or

     cargo run --bin client isaac

You should see an interactive prompt like:

   sugar > 

isaac > 

then, in each client, copy the x25519 key from the other as a contact (the excahnge x25519 keys):

     add isaac <isaac's_x25519_key>
     add sugar <sugar's_x25519_key>

then, send a message:

• in sugar client:

     send isaac Hello Isaac!

• in isaac client:

     receive