DLang docker images for CircleCi 2.0

[Seb]

tl;dr: you can now use special D docker images for CircleCi 2.0

---
version: 2
jobs:
   build:
     docker:
       - image: dlang2/dmd-circleci
---


Available tags
--------------

The default tag (`latest`) is the last stable release.

### DMD

```yaml
- image: dlang2/dmd-circleci:nightly
- image: dlang2/dmd-circleci:beta
- image: dlang2/dmd-circleci
- image: dlang2/dmd-circleci:2.078.0
```

### LDC

```yaml
- image: dlang2/ldc-circleci:beta
- image: dlang2/ldc-circleci
- image: dlang2/ldc-circleci:1.6.0
```

### GDC

```yaml
- image: dlang2/gdc-circleci
- image: dlang2/gdc-circleci:4.8.5
```

Full list:

- https://hub.docker.com/r/dlang2/dmd-circleci/tags/
- https://hub.docker.com/r/dlang2/ldc-circleci/tags/
- https://hub.docker.com/r/dlang2/gdc-circleci/tags/

This repo is fully automated and new releases get deployed 
automatically.
It already has DMD 2.078.0.

Repo: https://github.com/wilzbach/dlang-docker-circleci

Cheers,

Seb

PS: I'm aware of Stefan Rohe's great D Docker images [1], but 
this Docker image is built on top of the specialized CircleCi 
image (e.g. for their SSH login).

[1] https://github.com/lindt/docker-dmd