Random signatures for MirageOS, and an implementation using stdlib

mirage-random defines [Mirage_random.S][1] and [Mirage_random.C][2]
the signature for random-related devices for MirageOS.  It also
provides an implementation of `C` using `Random` from the OCaml standard
library.

[1]: https://mirage.github.io/mirage-random/Mirage_random.S.html
[2]: https://mirage.github.io/mirage-random/Mirage_random.C.html

### Installation

`mirage-random` can be installed with `opam`:

    opam install mirage-random

If you don't use `opam` consult the [`opam`](opam) file for build
instructions.

### Documentation

The documentation and API reference is automatically generated by
`ocamldoc` from the interfaces. It can be consulted [online][2].

[2]: https://mirage.github.io/mirage-random/Mirage_random.html