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.
Adds a wrapper for the glutin::Window which provides strongly typed
APIs and more convenient interfaces. Moves some gl calls into the
opengl-based renderer.
The point of most of the changes here is to clean up main().
Joe Wilm