Allow input via stdin and output via stdout

[alastair]

Hi,
We're using maw to search for similar copies of scans of 16th century printed music: https://f-tempo.org/
Searching Page-Images of Early Music Scanned with OMR: A Scalable Solution Using Minimal Absent Words

We're calling the maw binary on demand from our webserver to create words, and so found that it was helpful to be able to pass data in and read data directly from stdin/stdout instead of first writing it to a temporary file. Perhaps this would also be useful for others.