Removes FromMont and ToMont from field.Element api

[gbotrel]

See #276

[Tabaie]

Right, if these come from the standard docs they should be available in decimal or hex form.

[samlaf]

Trying to upgrade our version of gnark-crypto from 0.8 to 0.9.
We were using

config := ecc.MultiExpConfig{ScalarsMont: true}

whereas now MultiExpConfig does not have a ScalarsMont argument.

I see that the default was set to false in 0.8. Can I just remove that field and everything will work fine? Or will this lead to breaking changes?

Disclaimer: I don't know what montgomery form is.

[gbotrel]

That was actually an overlook on my sight, pointed by other users in the past;

there is actually a subtle breaking change here..

the default is now effectively ecc.MultiExpConfig{ScalarsMont: true} so if you used that everywhere, you should be fine.

But callers without an explicit value would have had the default at: ecc.MultiExpConfig{ScalarsMont: false} and the upgrade would be a silent change.. --> TLDR; all the APIs are now consistant and don't expose the underlying form / encoding of the field elements.

[samlaf]

That was actually an overlook on my sight, pointed by other users in the past;

there is actually a subtle breaking change here..

the default is now effectively ecc.MultiExpConfig{ScalarsMont: true} so if you used that everywhere, you should be fine.

But callers without an explicit value would have had the default at: ecc.MultiExpConfig{ScalarsMont: false} and the upgrade would be a silent change.. --> TLDR; all the APIs are now consistant and don't expose the underlying form / encoding of the field elements.

Awesome thanks! Small note: would have been useful if you guys added a Breaking Changes section to the release notes.
Otherwise is there a good reference that you would recommend to understand these montgomery forms and how they are used in this library?