accept file arguments

[gelisam]

file arguments were broken by #40, we should bring them back.

[ssadler]

Hmm... When was this actually needed?

[gelisam]

I never used it either. I opened this issue not because I needed the feature, but because we inherited this feature from hsp and one of my changes broke it.

[melrief]

I never used it either. It is from awk, that supports files as input. I think that loading a file directly in haskell instead of pipeline it can be faster and that's the only reason.

[gelisam]

Wow, nobody is using this, yet we religiously kept it alive?

Next time I accidentally break it, I suggest leaving it broken until a user complains :)