Nanoid

* Add `nanoid/async/format` and `nanoid/async/generate`.
* Improve synchronous API performance.
* Reduce `url` size (by Daniil Poroshin).
* Improve React Native docs (by joelgetaction).

* Reduce library size (by rqrqrqrq).

* Fix Node.js 6.11.1 support (by Andrey Belym).

* Speed up Node.js secure generators (by Dmitriy Tsvettsikh).

* Fix JSDoc (by Hendry Sadrak).

* Fix distribution in `nanoid/non-secure` (by Eatall).