Message: Support ICU MessageFormat using slexaxton/messageformat.js

:boom: WIP...

- [x] Implement #265
- [x] Plural generator
- [x] Functional tests
- [x] Docs
- [x] slexaxton/messageformat.js license ([debeaf4][])
- [x] example

[debeaf4]: https://github.com/SlexAxton/messageformat.js/blob/debeaf4/LICENSE
:+1:

>  [aka cldr-traverse, maybe]

:see_no_evil: I'm skipping that, but I'm adding a comment here to keep track of it https://github.com/rxaviers/cldrjs/issues/7#issuecomment-67639239