When debugging many issues, it's often very helpful to have the raw
glutin events printed out to stderr as they come in. This does that.
Note that since `glutin::Event` doesn't implement `Display`, we just use
rust's debugging output for now via `{:?}`.
This is part of an ongoing decoupling effort across the codebase and
tidying effort in main.rs. Everything to do with showing the window with
a grid of characters is now managed by the `Display` type. It owns the
window, the font rasterizer, and the renderer. The only info needed from
it are dimensions of characters and the window itself for sizing the
terminal properly. Additionally, the I/O loop has access to wake it up
when new data arrives.
This introduces the `cli` module and the `cli::Options` type. This type
holds all the options passable on the command line in addition to
providing arg parsing.
