Support Non-Composer Installs

[justincy]

Create an automated process that builds the gedcomx-php project into a .zip file that can be downloaded, including dependencies needed to run the project. The purpose of this is to enable developers to use the SDK even if they do not have access to install SDK via Composer.

This process should run for every new release committed to Github. This could be done via a Travis-CI process. The zip file should be distributed with a version number of some sort that can allow developers to download older versions of the SDK if needed, but also download the latest build. Take a look at the Dropbox PHP SDK for an example of desired packaging.

https://www.dropbox.com/developers/core/sdks/php

_{Copied from FamilySearch/gedcomx-php#27}

[justincy]

Could we generate a phar instead? Generating a phar would be more complicated but it would be easier for the user to install because it's just one file.

[justincy]

When a new release is cut, GitHub automatically generates a zip file for us.