Add stdio mode support

[leonbohn]

It would be great if it were possible to write a LaTeX file to STDIN of tex-fmt and have it write the formatted code to its STDOUT.

Unless there are any objections to this functionality, I will try to implement it myself, probably as a switch (--stdin) which bypasses iterating through the provided file names and instead just reads a single file from STDIN. This would, of couse, implicitly also set the --print flag and dump the formatted code to STDOUT.

[WGUNDERWOOD]

This sounds good to me -- feel free to implement it and submit a pull request!

[leonbohn]

Great :) I've tried implementing something and opened the PR #21 .