resources: Add JavaScript transpiling solution

Add a new pipe called TranspileJS which uses the Babel cli. This makes it possible for users to write ES6 JavaScript code and transpile it to ES5 during website generation so that the code still works with older browser versions.

Fixes #5764

docs/content/en/hugo-pipes/transformjs.md

@@ -0,0 +1,69 @@
+---
+title: TransformJS
+description: Hugo Pipes can process JS files with Babel.
+date: 2019-03-21
+publishdate: 2019-03-21
+lastmod: 2019-03-21
+categories: [asset management]
+keywords: []
+menu:
+  docs:
+    parent: "pipes"
+    weight: 75
+weight: 75
+sections_weight: 75
+draft: false
+---
+
+Any JavaScript resource file can be transpiled to another JavaScript version using `resources.TransformJS` which takes for argument the resource object and a slice of options listed below. TransformJS uses the [babel cli](https://babeljs.io/docs/en/babel-cli).
+
+
+{{% note %}}
+Hugo Pipe's TranspileJS requires the `@babel/cli` and `@babel/core` JavaScript packages to be installed in the environment (`npm install -g @babel/cli @babel/core`) along with any Babel plugin(s) or preset(s) used (e.g., `npm install -g @babel/preset-env`).
+
+If you are using the Hugo Snap package, Babel and plugin(s) need to be installed locally within your Hugo site directory, e.g., `npm install @babel/cli @babel/core` without the `-g` flag.
+{{% /note %}}
+### Options
+
+config [string]
+: Path to the Babel configuration file
+
+_If no configuration file is used:_
+
+plugins [string]
+: Comma seperated string of Babel plugins to use
+
+presets [string]
+: Comma seperated string of Babel presets to use
+
+minified [bool]
+: Save as much bytes as possible when printing
+
+noComments [bool]
+: Write comments to generated output (true by default)
+
+compact [string]
+: Do not include superfluous whitespace characters and line terminators (true/false/auto)
+
+verbose [bool]
+: Log everything
+
+### Examples
+Without a `.babelrc` file, you can simply pass the options like so:
+```go-html-template
+{{- $transpileOpts := (dict "presets" "@babel/preset-env" "minified" true "noComments" true "compact" "true" ) -}}
+{{- $transpiled := resources.Get "scripts/main.js" | transpileJS $transpileOpts -}}
+```
+
+If you rather want to use a config file, you can leave out the options in the template.
+```go-html-template
+{{- $transpiled := resources.Get "scripts/main.js" | transpileJS $transpileOpts -}}
+```
+Then, you can either create a `.babelrc` in the root of your project, or your can create a `.babel.config.js`.
+More information on these configuration files can be found here: [babel configuration](https://babeljs.io/docs/en/configuration)
+
+Finally, you can also pass a custom file path to a config file like so:
+```go-html-template
+{{- $transpileOpts := (dict "config" "config/my-babel-config.js" ) -}}
+{{- $transpiled := resources.Get "scripts/main.js" | transpileJS $transpileOpts -}}
+```