IO#skip returns the number of bytes it skipped

[carlhoerberg]

Can make some code much better looking, eg:

len = Int32.from_io @file
@file.skip(len)
skipped += len

can become

skipped += @file.skip(Int32.from_io(@file))

[carlhoerberg]

Would also suggest increasing the buffer to 8kb as done in IO.copy. Can add it here or create another PR.

[straight-shoota]

Looks good, but you'll need to add specs for this.
Buffer size should be a separate issue.

[RX14]

For #skip I don't see the point because it's guaranteed to be the amount specified. For #skip_to_end it's definitely useful.

[carlhoerberg]

Correct, but it allows for shorter user code, see example above. Do have a reason why not to return it?

[bcardiff]

The return type of these methods should be UInt64. This will match #7660.