Update and structure validator API

[bitkidd]

This proposal suggests to clean up the api by splitting the roles of methods, removing options from schemes and grouping them into corresponding groups: rules or a new group - modifiers, that takes the role of value mutation.

Full Rendered Proposal
Discussion Thread

[thetutlage]

@targos @RomainLanz What you guys think?

[targos]

I'm generally ok with the approach.
I'd still like us to find a way to help the user select the right rules (so they have an error when adding a string rule or modifier to a number field, or even better if we can prevent intellisense from suggesting wrong ones)