Rust API for Linux Direct Rendering Manager and Kernel Modesetting

The crate linux-drm wraps linux-io to provide more convenient access to the Linux DRM/KMS API without depending on any C libraries.

This is currently experimental and the API is likely to change before becoming stable in a 1.0 release as we explore different API designs.

In particular, the ioctl module currently exposes some IOCTL requests that are unsound because they allow safe Rust to ask the kernel to write to arbitrary pointers. Dealing with this will likely require some new features in the underlying linux-io crate, but for now the focus is on designing the higher-level API that wraps the raw IOCTL requests.

This crate also currently relies on some unstable features and is therefore only usable on a nightly Rust toolchain.