Add option to just preprocess file and print output

[dedmen]

I tried to add a --verbose parameter to binarize but because the preprocessor can only print to a file handle I'd have to duplicate every output to also print to stdout.
Or read the file in again and print that which is a bit too cumbersome.

And to make a preprocess option I'd have to print to a temp file and read it instead instead of being able to do it in memory.
Implementing it like that feels too crusty to me so I rather let that be done by people who know this C stuff.