Adding a new formatter

Add a etc/config/compiler-explorer.local.properties file
- Add a new formatter under the formatters key
- The new formatter can have the following keys: name, exe, styles, type, explicitVersion (to override version parsing), version (argument to get version info), versionRe (regex to filter out the right version info)
- Add a lib/formatters/<formatter>.js file using the template below, replacing Type and type as appropriate
```
import { BaseFormatter } from '../base-formatter';

export class TypeFormatter extends BaseFormatter {
    static get key() { return 'type'; }
}
```
- The value returned by key above corresponds to the type property you set in the compiler-explorer properties configuration file.
- Tweak format(source, options) and isValidStyle(style) as necessary. See the JSDoc for format and the implementations for other formatters to get a further understanding of how to implement format(source, options).
Add your TypeFormatter to lib/formatters/_all.js in alphabetical order
You can check the output of http://localhost:10240/api/formats to be sure your formatter is there.
Make an installer in the infra repository. An example patch for adding an installer can be found here

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