OCI command-line API

The OCI Specifications currently focus on the bundle-author ↔ runtime interface, but there is renewed interest in specifying a command-line API for the runtime-caller ↔ runtime interface. A common command-line API would make it easier to build higher-level tools that are runtime-agnostic (e.g. conformance testers like ocitools). This repository contains initial work on that API, with more detailed discussion in this thread. The usual development rules apply, and the legal stuff is spelled out here. The target for the inital design will be to match the lifecycle pull request, keeping as much similarity with the existing runC command-line as possible.