Add decode-to-file function

[oadams]

Wraps decode and writes the hypotheses to a text file, or latex source file.

[shuttle1987]

What's needed to get this completed?

[oadams]

The code I committed some time back which broke the interface: Just a wrapper to the decode function that then writes the returned text to a file. When I add it back in I'll just call it decode_to_file instead of decode.