Add global keywords config option

[ssalbdivad]

Could be used like:

import { configure } from "arktype/config"

configure({
    keywords: {
       "string.email": { message: () => "INVALID EMAIL" }
    }
})

As opposed to:

import { keywords, scope } from "arktype"

const { type } = scope({
    string: scope({
        ...keywords.string,
        email: keywords.string.email.configure({
            message: () => "INVALID EMAIL"
        })
    }).export()
})

// INVALID EMAIL
type("string.email")("foo").toString() //?