Support for STDIN chaining (pipes)

I'm trying to do something like this:

```
cat ${file} | sed 's,# REMOVE THESE LINES.*,,g' | cr --format plain
```

`cr` doesn't appear to read from STDIN, so cannot be chained like this.  While I can create a temporary file, I'd rather not so as to keep the file system clean in the event of a script failure.
