docs(config): update target.md (#1262)

Add documentation on passing a function for `target`. Also 
include some minor tweaks and formatting improvements.

Author: jchip

content/configuration/target.md

@@ -9,24 +9,57 @@ contributors:
   - pastelsky
 ---
 
-webpack can compile for multiple environments or _targets_. To understand what a target is in detail, read [the concepts](/concepts/targets).
+webpack can compile for multiple environments or _targets_. To understand what a `target` is in detail, read through [the targets concept page](/concepts/targets).
 
 ## `target`
 
-`string`
+`string | function(compiler)`
 
-Tells webpack which environment the application is targeting. The following values are supported via [`WebpackOptionsApply`](https://github.com/webpack/webpack/blob/master/lib/WebpackOptionsApply.js):
+Intructs webpack to target a specific environment.
 
-| `target`      | Description            |
-| ------------- |------------------------|
-| `async-node`| Compile for usage in a Node.js-like environment (uses `fs` and `vm` to load chunks asynchronously)    |
-| ~~`atom`~~      | Alias for `electron-main` |
-| ~~`electron`~~      | Alias for `electron-main` |
-| `electron-main`      | Compile for [Electron](http://electron.atom.io/) for main process. |
-| `electron-renderer`      | Compile for [Electron](http://electron.atom.io/) for renderer process, providing a target using `JsonpTemplatePlugin`, `FunctionModulePlugin` for browser environments and `NodeTargetPlugin` and `ExternalsPlugin` for CommonJS and Electron built-in modules. |
-| `node` | Compile for usage in a Node.js-like environment (uses Node.js `require` to load chunks) |
-|`node-webkit`|  Compile for usage in WebKit and uses JSONP for chunk loading. Allows importing of built-in Node.js modules and [`nw.gui`](http://docs.nwjs.io/en/latest/) (experimental) |
-|`web`| Compile for usage in a browser-like environment **(default)** |
-|`webworker`| Compile as WebWorker |
+
+### `string`
+
+The following string values are supported via [`WebpackOptionsApply`](https://github.com/webpack/webpack/blob/master/lib/WebpackOptionsApply.js):
+
+Option                | Description
+--------------------- | -----------------------
+`async-node`          | Compile for usage in a Node.js-like environment (uses `fs` and `vm` to load chunks asynchronously)
+~~`atom`~~            | Alias for `electron-main`
+~~`electron`~~        | Alias for `electron-main`
+`electron-main`       | Compile for [Electron](http://electron.atom.io/) for main process.
+`electron-renderer`   | Compile for [Electron](http://electron.atom.io/) for renderer process, providing a target using `JsonpTemplatePlugin`, `FunctionModulePlugin` for browser environments and `NodeTargetPlugin` and `ExternalsPlugin` for CommonJS and Electron built-in modules.
+`node`                | Compile for usage in a Node.js-like environment (uses Node.js `require` to load chunks) |
+`node-webkit`         | Compile for usage in WebKit and uses JSONP for chunk loading. Allows importing of built-in Node.js modules and [`nw.gui`](http://docs.nwjs.io/en/latest/) (experimental)
+`web`                 | Compile for usage in a browser-like environment **(default)**
+`webworker`           | Compile as WebWorker
 
 For example, when the `target` is set to `"electron"`, webpack includes multiple electron specific variables. For more information on which templates and externals are used, you can refer to webpack's [source code](https://github.com/webpack/webpack/blob/master/lib/WebpackOptionsApply.js#L70-L185).
+
+
+### `function`
+
+If a function is passed, then it will be called with the compiler as a parameter. Set it to a function if none of the predefined targets from the list above meet your needs.
+
+For example, if you don't want any of the plugins they applied:
+
+```js
+const options = {
+  target: () => undefined
+};
+```
+
+Or you can apply specific plugins you want:
+
+```js
+const webpack = require("webpack");
+
+const options = {
+  target: (compiler) => {
+    compiler.apply(
+      new webpack.JsonpTemplatePlugin(options.output),
+      new webpack.LoaderTargetPlugin("web")
+    );
+  }
+};
+```