Compatiblity with JJChiDguez/sibc

Hi,

First of all thank you very much for this awesome library!

Im currently working on a Go project which has to work with SCIDH keys generated by [sibc](https://github.com/JJChiDguez/sibc).
I'd like to use this library for the Go part, but I couldn't get them to work together.

I've opened [an issue in the repo](https://github.com/JJChiDguez/sibc/issues/11) of the sibc library, if they are compatible at all and here's the answer of the maintainer:

> Hello there!
>
> It's good to read you are enjoying and using the library. I hope this library helps increase the use of isogeny-based primitives (at least, as a toolkit for learning/using isogenies in practice).
>
> Answering
>
> > Do you know if these libraries are even compatible at all?
>
> In summary, both libraries are not directly compatible; see below the main difference:
>
> 1. The Go-code is doing a non-constant-time implementation of **csidh** (at least at field operation level).
> 2. The keyspace from the Go-code is `[-5,5]⁷⁴ ≈ 2²⁵⁶`, that is, private keys are integer vectors `e` with entries `eᵢ` in `[-5,5]`. On the other hand, **sibc** works with "optimal" bound vectors, that is, `eᵢ` is an integer in `[-mᵢ, mᵢ]` where each `mᵢ` is fixed and possibly different from another `mⱼ`.
> 3. In the Go-code private keys are arrays of `37=74/2` bytes (see `var privateOut [37]byte`), while in the csidh-default configuration of **sibc**, this array has length `74`.
>
> As a consequence, private keys generated by the Go-code are not compatible with the private keys from **sibc** because of
>
> 1. Different private key entry ranges: `eᵢ` is an integer in `[-mᵢ, mᵢ]`. For instance, **sibc** use [these bounds](https://github.com/JJChiDguez/sibc/blob/master/sibc/data/exponents/mitm/128/wd2/e5);
> 2. Different array lengths (I think this is the main issue why **sibc** is failing, it tries to access to (for example) the 38th entry of `e,` but it fails because the Go-code output has just 37 entries).

Since I'm not experienced with SCIDH I'd like to ask if it would be possible to make these two libraries compatible and if so, how hard it would be?

Thanks in advance!