Fixes #127

This commit introduces two different validation modes:
- Strict (default): Only allows letters, digits, hyphens
- Lax: Allows any octets and just checks for the max lengths

This allows domains to have an underscore character. Closes #134

BREAKING CHANGE: Introduces a dependency on the global `TextEncoder` constructor which should be available in all modern engines
(see https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder). The strict validation mode (which is the default) will also be a little bit more strict since it will now also check for hyphens at the beginning or end of a domain label. It also requires top-level domain names not to be all-numeric.

# [5.0.0](v4.1.0...v5.0.0) (2022-01-23)

### Bug Fixes

* Type errors with is-ip module ([8ea728c](8ea728c))

### Features

* Improve validation ([171a8c8](171a8c8))

### BREAKING CHANGES

* Introduces a dependency on the global `TextEncoder` constructor which should be available in all modern engines
(see https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder). The strict validation mode (which is the default) will also be a little bit more strict since it will now also check for hyphens at the beginning or end of a domain label. It also requires top-level domain names not to be all-numeric.