Just been doing some thinking about this. I think that using STDIN as a default is a good thing for the most part. 

A command such as `eyaml -e -s "test value"` can just as easily be `echo -n "test value" | eyaml -e` (or any other combination).  STDIN can also be used to read from files: `eyaml -e < mykeytoencrypt.pem`.

The hanging can apparently be fixed by checking STDIN.tty? which will tell if a terminal is connected to STDIN or not and reading STDIN can be ignored if we are connected to a terminal.