[v3] Implement new Concept Exercise: anonymous-functions

This issue describes how to implement the `anonymous-functions` concept exercise for the Clojure track.

## Getting started

**Please please please read the docs before starting.** Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read up on the following documents:

- [The features of v3](https://github.com/exercism/v3/blob/master/docs/concept-exercises.md).
- [Rationale for v3](https://github.com/exercism/v3/blob/master/docs/rationale-for-v3.md).
- [What are concept exercise and how they are structured?](https://github.com/exercism/v3/blob/master/docs/features-of-v3.md)

Please also watch the following video:

- [The Anatomy of a Concept Exercise](https://www.youtube.com/watch?v=gkbBqd7hPrA).

## Goal

The goal of this exercise is to teach the student how to use anonymous functions in Clojure.

## Learning objectives

The student will learn:

- Creating anonymous functions with `fn`
- Shorthand reader syntax (`#`, `%`, `%&`, etc.)

## Out of scope

- Higher-order functions

## Concepts

- `anonymous-functions`
- `evaluation`
- `functions`
- `rest-parameters`

## Prerequisites

- `basic-functions`
- `variadic-functions`

## Resources to refer to

### Hints

- [Clojure Guide: Functions](https://clojure.org/guides/learn/functions)

### After

- [clojure-doc.org - Functions in Clojure](http://clojure-doc.org/articles/language/functions.html#variadic-functions)

## Representer

This exercise does not require any modifications to the track's representer.

## Analyzer

This exercise does not require any modifications to the track's analyzer.

## Implementing

To implement a concept exercise, the following files must be created:

```
languages
└── clojure
└── exercises
└── concept
└──
├── .docs
| ├── instructions.md
| ├── introduction.md
| ├── hints.md
| └── after.md (optional)
├── .meta
| |── design.md
| └── Example.clj
├── .clj
└── _test.clj
```

## Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.

Beginne mit dem Lesen von docs/concept-exercises.md, docs/rationale-for-v3.md und docs/features-of-v3.md und sieh dir anschließend das verlinkte Video Anatomy of a Concept Exercise an. Erstelle die aufgeführten Dateien unter languages/clojure/exercises/concept/anonymous-functions und decke die angegebenen Lernziele und Voraussetzungen ab. Als erledigt gilt die Aufgabe, wenn Übung, Tests, Metadaten und Dokumentation vorhanden sind, ohne Änderungen an representer oder analyzer.

Vom Indexierungsmodell aus dem Issue-Text verfasst.