Lwt module type definitions for Mirage-compatible applications

This is a virtual package that pulls in all the concrete
dependencies required for the `mirage-types.lwt` ocamlfind
package to become available.

The purpose of this library is to provide concrete types
for several that are left abstract in `mirage-types`:

- `type 'a io = 'a Lwt.t`
- `type page_aligned_buffer = Io_page.t`
- `type buffer = Cstruct.t`
- `type macaddr = Macaddr.t`
- `type ipv4addr = Ipaddr.V4.t`
