Change default behavior

[MatthewScholefield]

When run without any arguments, mimic accepts input from stdin. While this may be useful for process interaction via piping, it is confusing to users since it looks like mimic is just lagging (plus, ctrl+c doesn't get out of it since only EOF/ctrl-D finishes the stream). I was thinking it would be better to do one of the following:

1. mimic shows help and mimic - or mimic -s inputs from stdin
2. Keep behavior, but check for when run in a terminal (not a pipe) and display help when that happens.