Documentation discrepancy

[cailloumajor]

Hello. First of all, thank you for those great libraries.

Unless I misunderstand, the statements of lines 135-140 in the extract below do not reflect how the code is doing.

https://github.com/3Hren/msgpack-rust/blob/f4ad0d0257edfea460eb176cdb7d11ddfe97ba3b/rmp/src/encode/sint.rs#L132-L170