Reorganize and rewrite examples

This commit is a large-ish scale reorganization of our examples. The
main goal here is to have a dedicated section of the guide for example,
and all examples will be listed there. Each example's `README` is now
just boilerplate pointing at the guide along with a blurb about how to
run it.

Some examples like `math` and `smorgasboard` have been deleted as they
didn't really serve much purpose, and others like `closures` have been
rewritten with `web-sys` instead of hand-bound bindings.

Overall it's hoped that this puts us in a good and consistent state for
our examples, with all of them being described in the guide, excerpts
are in the guide, and they're all relatively idiomatically using
`web-sys`.

guide/src/web-sys/examples/2d-canvas.md

@@ -1,29 +0,0 @@
-# 2D Canvas
-
-Drawing a smiley face with the 2D canvas API. This is a port of part of [this
-MDN
-tutorial](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Drawing_shapes#Moving_the_pen)
-to `web-sys`.
-
-[See the full source at
-`wasm-bindgen/examples/canvas`.](https://github.com/rustwasm/wasm-bindgen/tree/master/examples/canvas)
-
-![A smiley face](./2d-canvas.png)
-
-## `Cargo.toml`
-
-The `Cargo.toml` enables features necessary to query the DOM and work with 2D
-canvas.
-
-```toml
-{{#include ../../../../examples/canvas/Cargo.toml}}
-```
-
-## `src/lib.rs`
-
-Gets the `<canvas>` element, creates a 2D rendering context, and draws the
-smiley face.
-
-```rust
-{{#include ../../../../examples/canvas/src/lib.rs}}
-```

guide/src/web-sys/examples/fetch.md

@@ -1,23 +0,0 @@
-# The `fetch` API
-
-This example uses the `fetch` API to make an HTTP request to the GitHub API and
-then parses the resulting JSON.
-
-[See the full source at
-`wasm-bindgen/examples/fetch`.](https://github.com/rustwasm/wasm-bindgen/tree/master/examples/fetch)
-
-## `Cargo.toml`
-
-The `Cargo.toml` enables a number of features related to the `fetch` API and
-types used: `Headers`, `Request`, etc. It also enables `wasm-bindgen`'s `serde`
-support.
-
-```toml
-{{#include ../../../../examples/fetch/Cargo.toml}}
-```
-
-## `src/lib.rs`
-
-```rust
-{{#include ../../../../examples/fetch/src/lib.rs}}
-```

guide/src/web-sys/examples/index.md

@@ -1,3 +0,0 @@
-# Examples of using `web-sys`
-
-This subsection contains examples of using the `web-sys` crate.

guide/src/web-sys/examples/paint.md

@@ -1,24 +0,0 @@
-# Paint
-
-A simple painting program.
-
-[See the full source at
-`wasm-bindgen/examples/paint`.](https://github.com/rustwasm/wasm-bindgen/tree/master/examples/paint)
-
-## `Cargo.toml`
-
-The `Cargo.toml` enables features necessary to work with the DOM, events and
-2D canvas.
-
-```toml
-{{#include ../../../../examples/paint/Cargo.toml}}
-```
-
-## `src/lib.rs`
-
-Creates the `<canvas>` element, applies a CSS style to it, adds it to the document,
-get a 2D rendering context and adds listeners for mouse events.
-
-```rust
-{{#include ../../../../examples/paint/src/lib.rs}}
-```

guide/src/web-sys/examples/web-audio.md

@@ -1,36 +0,0 @@
-# WebAudio
-
-This example creates an [FM
-oscillator](https://en.wikipedia.org/wiki/Frequency_modulation_synthesis) using
-the [WebAudio
-API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API) and
-`web-sys`.
-
-[See the full source at
-`wasm-bindgen/examples/webaudio`.](https://github.com/rustwasm/wasm-bindgen/tree/master/examples/webaudio)
-
-## `Cargo.toml`
-
-The `Cargo.toml` enables the types needed to use the relevant bits of the
-WebAudio API.
-
-```toml
-{{#include ../../../../examples/webaudio/Cargo.toml}}
-```
-
-## `src/lib.rs`
-
-The Rust code implements the FM oscillator.
-
-```rust
-{{#include ../../../../examples/webaudio/src/lib.rs}}
-```
-
-## `index.js`
-
-A small bit of JavaScript glues the rust module to input widgets and translates
-events into calls into wasm code.
-
-```js
-{{#include ../../../../examples/webaudio/index.js}}
-```

guide/src/web-sys/examples/webgl.md

@@ -1,25 +0,0 @@
-# 2D Canvas
-
-This example draws a triangle to the screen using the WebGL API.
-
-[See the full source at
-`wasm-bindgen/examples/webgl`.](https://github.com/rustwasm/wasm-bindgen/tree/master/examples/webgl)
-
-## `Cargo.toml`
-
-The `Cargo.toml` enables features necessary to obtain and use a WebGL
-rendering context.
-
-```toml
-{{#include ../../../../examples/webgl/Cargo.toml}}
-```
-
-## `src/lib.rs`
-
-This source file handles all of the necessary logic to obtain a rendering
-context, compile shaders, fill a buffer with vertex coordinates, and draw a
-triangle to the screen.
-
-```rust
-{{#include ../../../../examples/webgl/src/lib.rs}}
-```