This adds the following new features and options:- `generateMessageIds`: Will generate the message descriptor `id`based on a SHA1 hash of the `defaultMessage` and `description`.- `removeExtractedData`: Will remove the `defaultMessage` and`description` from the message declaration to save k-weight.- `enforceDescriptions`: Requires that all declared messages _must_contain a `description` for translators.In order to generate the message IDs in a stable way, the ICUmessages are parsed and pretty-printed into a standard format whichremoves any insignificant whitespace. This is also used to validatethat the ICU Message syntax to make sure it's correct.