fix: Expose format errors functions

[gillchristian]

This PR fixes the breaking change introduced in #17 (#17 (review)).

Also exports a Reporter as default (see: https://gcanti.github.io/io-ts/modules/PathReporter.ts.html) and a short example in the README.md

[hasparus]

This formatValidationErrors is way better than the one I was using!

import { compact } from "fp-ts/lib/Array";
import { Errors } from "io-ts";
import { formatValidationError } from "io-ts-reporters";

export const formatValidationErrors = (errors: Errors) =>
  compact(errors.map(formatValidationError));

Thanks! 🙏

[gillchristian]

@hasparus released on v1.2.0.