Add dump to file option

[MatthewTingum]

I can enumerate files in a ubi archive with:
ubidump -l bar.ubi

Then I can try to extract a binary file with:
ubidump -c foo.bin bar.ubi > foo.bin

But I end up with three lines of text preceding the binary.
These lines are output of the program itself.
The lines have to be manually stripped out.
Perhaps an -o option for outputting to a file?

Over-scoping a little bit, but I'd like to see an "extract all" option too.

Mounting doesn't work great on WSL 1 (If one were to get at the contents that way).
binwalk doesn't seem to extract the ubi format IIRC.
This could be a great addition to binwalk with a little work.

I'll be glad to make a pull request if there's an active maintainer.

[MatthewTingum]

Ah, I see this option now:

  --savedir DIRECTORY, -s DIRECTORY
                        save files in all volumes to the specified directory

Maybe a simple README update is in order.

[MatthewTingum]

I have opened a pull request that updates the README.

Still, extracting a single file is not particularly convenient.
Consider making the cat option only output file contents to stdout.
No informational text in the stdout.
Only errors in stderr.
Just a thought.