We need high level bindings for integrity

[jbaublitz]

For integrity support, we will first need high level binding support for dm-integrity in this library. We should probably get a head start on it.

@mulkieran Would you prefer to take this or do you want me to?

[mulkieran]

We might want to consider doing a redesign of our outer layer. It is overconstrained and awkward. Alternatively, we could consider only using the core part of devicemapper-rs.