Export class Errors correcty

What's Changed

• Export errors correctly by @alexbol99 in #158
  Class Error exported now, one can check flatten-js errors like this:

import {Errors, vector} from "@flatten-js/core";

try {
    const v = vector(0,0)
    v.normalize()
}
catch (e) {
    console.log(e.message === Errors.ZERO_DIVISION.message)
}

• Related issue
  Errors export #157 by @edemaine

Full Changelog: v1.4.5...v1.4.6