String identity template tag

[Isiah Meadows]

It'd be *way* easier to construct simple template tags if there was a
built-in identity tag, like this:

```js
String.identity = (template, ...args) => {
    let str = ""
    for (let i = 0; i < args.length; i++) {
        str += template[i] + String(args[i])
    }
    return str + template[template.length - 1]
}
```

This would also provide some language consistency in that tag-less
templates are evaluated as if they were tagged with the internal
`String.identity`.

The usefulness of this is for simple utility template tags, like:

- `` debug`Value: ${value}` ``, where `value` is auto-inspected.
- `` trust`html` ``, which returns a raw HTML virtual DOM node.
- `` escape`trusted ${untrusted}` ``, which escapes template variables

Here's how `debug` and `trust` above would be implemented:

```js
// `debug` - logs a message with inspected values to the console
const debug = (template, ...args) =>
    String.identity(template, ...args.map(arg => util.inspect(arg)))

// `trust` - returns a Mithril `m.trust` vnode
// https://mithril.js.org/trust.html
const trust = (...args) =>
    m.trust(String.identity(...args))

// `escape` - logs a message with inspected values to the console
const escape = (template, ...args) =>
    String.identity(template, ...args.map(escapeString))
```

-----

Isiah Meadows
contact at isiahmeadows.com
www.isiahmeadows.com