Fix non interactive prompts in Ubuntu

Implicit installation of certain packages like `tzdata` causes `docker build` to block, even when employing a `DEBIAN_FRONTEND=noninteractive` environment variable. Since special casing all problematic packages is a futile endeavor, we are globally configuring deb to be non interactive. Unfortunately this setting will persist into the container runtime.

Fix broken 0.15 binaries

By updating the build environment to Ubuntu 20.04 in d4508a9, bundled dependencies did no longer match Traveling Ruby's version (2.7 vs 2.3). Moreover, `Array#append` was added in Ruby 2.5 and thus not available in Ruby 2.3

Support for environments without TTY

By passing `--no-tty` to mini-cross, `docker run` will be instructed to not assume a TTY environment. This enables the usage of mini-cross in CI situations without a full TTY like Jenkins an Github Actions.

Mixin support

mini-cross now supports mixins which enable reuse of common configuration.

Support for Arch Linux

`ArchDockerContext` adds support for isolated development environments based on Arch Linux.

Enable installation of PHP in Ubuntu 18.04

Unfortunately, the implicit installation of tzdata causes the Docker image build process to block, even when employing DEBIAN_FRONTEND=noninteractive. Therefore I'm forced to manually install tzdata on every build in order to allow installation of PHP in Ubuntu 18.04 😞

Support for Debian

Tested with Wheezy, Jessie and Stretch.

Making mini-cross installable through npm

Cross distribution package installation is still an unsolved problem.
While where are many solutions like flatpack, non gained enough traction
to yet.

Nevertheless, since mini-cross appeals to developers, there's a high
likeliness npm is already installed. Therefore I'm making mini-cross
installable through npm

```
npm install -g mini-cross
```

This will install the `mc` binary into your system path. Multiple
versions can be chosen from on the command line e.g.

```
npm install -g mini-cross@0.11.1
```

Since docker already requires `linux-x86_64` the node package only
includes that target.

Added publish instruction

It's now possible to add port forwardings using the `publish` instruction, e.g.:

````yaml
---
base: ubuntu:16.04
install:
 - apache2
publish:
 - 8080:80
---
````

All current [publication formats](https://docs.docker.com/engine/reference/run/#expose-incoming-ports) of docker are supported.

Test all supported operating systems

Previously only one Fedora and one Ubuntu version was tested. Now the smoke test is executed on all supported operating system versions:

 * Fedora 24
 * Fedora 25
 * Fedora Rawhide
 * Ubuntu 14.04
 * Ubuntu 16.04
 * Ubuntu 16.10
 * Ubuntu 17.04