Function for PUT request on file object

[IvanAnishchuk]

Especially for moving file to another directory and renaming, but other options (like description and tags) shouldn't hurt as well: http://developers.box.com/docs/#files-update-a-files-information

It almost like sharing a file, so shouldn't be hard to implement. Or I can try to send a patch (if we decided to use your library in our project instead of our own implementation). Thanks anyway.

[tals]

Hey :)

If you're willing to add it (+ tests), I'd be glad to merge it back in.
It should be easy to add, as it's pretty simple stuff.