Add docker support to help building dist files

[mstred]

Hi @gregjacobs... although you're the one supposed to be building the project's dist files, I think it would be kinda helpful to use an easier step to achieve that, either for yourself or even for particular forks of Autolinker.

In this PR, I'm adding a Dockerfile which uses a base image with node and ruby (due to jsduck), a .dockerignore and a docker-compose.yml file with an example of how to use it.

Feel free to add any suggestions or even improvements on this.

[gregjacobs]

Hey @mstred, thanks for the PR. I was just thinking: JSDuck was a great documentation generator, but unfortunately it seems abandoned at this point and doesn't support TypeScript (of which I'd like to update Autolinker to). Would it be helpful for me to just remove the JSDuck dependency?

[mstred]

That was the only reason I looked for some way to put both node and ruby in the same base image, as it's required for JSDuck to be installed as a ruby gem. Removing it from the actual stack would make ir even leaner.
However, when trying to run npm install over a pure node-based docker image, gulp-jsduck post-install hook will look for a jsduck gem executable and it'll fail, as it won´t be able to find it in an environment without rubygems.

Here's an snippet of what happens in this situation:

$ npm i
npm WARN deprecated gulp-util@2.2.20: gulp-util is deprecated - replace it, following the guidelines at https://medium.com/gulpjs/gulp-util-ca3b1f9f9ac5
npm WARN deprecated gulp-util@3.0.8: gulp-util is deprecated - replace it, following the guidelines at https://medium.com/gulpjs/gulp-util-ca3b1f9f9ac5
npm WARN deprecated http2@3.3.7: Use the built-in module in node 9.0.0 or newer, instead
npm WARN deprecated connect@2.30.2: connect 2.x series is deprecated
npm WARN deprecated graceful-fs@3.0.11: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated minimatch@0.2.14: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated graceful-fs@1.2.3: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js

> jsduck@0.2.1 install /srv/Autolinker.js/node_modules/jsduck
> npm run-script configure


> jsduck@0.2.1 configure /srv/Autolinker.js/node_modules/jsduck
> node scripts/configure.js

Configuring JSDuck
Could not find jsduck. Attempting to install.
Could not find gem executable.
Please manually install JSDuck.