[RFC] Window building

[kvark]

Currently, we sort-of re-implement a small fraction of glutin::WindowBuilder in our three::Builder. Given that glutin just re-exports winit, and that one is cross-platform and used by gfx-rs's windowing crates, I believe we should be basing around it.

There are only 2 properties we need (so far) outside of winit stuff: vertical sync and shader path. Perhaps, we could make this work like:

struct WindowSettings {
  pub builder: winit::WindowBuilder,
  pub vsync: bool,
  pub shader_path: Option<PathBuf>,
}

impl Window {
  fn new(title: Into<String>) -> Self {}
  fn from_settings(ws: WindowSettings) -> Result<Self, OurError> {}
}

The second choice would be for clients who need to fine-tune everything, and they can handle the error if something goes wrong.

[vitvakatu]

The thing I like in our current design is that it needs just a few steps to adjust some settings.
For example, it's common situation for me when I need to load shaders from some path for some example. With current design, all I need is:

1. change new to builder
2. add new shader_directory(...) function call
3. end up with build()

With this approach I would need to add new WindowSettings struct, set up winit::WindowBuilder and change new(...) to from_settings(...).unwrap().

[alteous]

As stated in #129, I think the display/windowing system should be independent of the rest of the crate features, but that's sort of off-topic.