Compatibility library for OCaml's Uchar module

The `uchar` package provides a compatibility library for the
[`Uchar`][1] module introduced in OCaml 4.03.

The `uchar` package is distributed under the license of the OCaml
compiler. See [LICENSE](LICENSE) for details.

[1]: http://caml.inria.fr/pub/docs/manual-ocaml/libref/Uchar.html

