shiny/driver/windriver: new package providing a Windows driver

This provides the initial implementation of a Windows driver for shiny.
It will only open a window and wait for you to close it; Buffer and
Texture will come next, when I figure out how they will work.

I tried to lay down the design of the package in doc.go. If you are still
confused, I'll be glad to rewrite or expand it.

Currently this uses cgo.

Patch set 2 changes the C formatting to match the Go sourcce tree's.
It also includes a quick change to driver_fallback.go.

Patch set 3 rewrites doc.go, hopefully to be clearer.

Patch set 4 implements changes suggested in code review and
removes a block of comments that was accidentally left in
when doc.go was written.

Patch set 5 formats this commit message.

Change-Id: I2b060455243f445dd0f4c62f6f0c346768491547
Reviewed-on: https://go-review.googlesource.com/13617
Reviewed-by: Nigel Tao <nigeltao@golang.org>
11 files changed