Publish API documentation to gh-pages on every push to develop

[pdavidc]

Description of the Change

Publish the WorldWindJava API documentation to the built-in GitHub pages site after every push to develop. The resultant documentation is immediately available online and always up-to-date. The WorldWind website links to this documentation from the Java documentation page.

https://NASAWorldWind.github.io/WorldWindJava

Why Should This Be In Core?

See description.

Benefits

See description.

Potential Drawbacks

None.

Applicable Issues

Closes #142

[zglueck]

Looks Good!

[AndrewTasso]

Does this mean that the default linked documentation is for the develop branch now? I would expect the main site to link to the latest stable javadoc and not the development version. Additionally, would this change mean that the published javadoc would be out of sync with releases?

[eirizarry]

@AndrewTasso, to clarify, the default linked documentation has always been for the develop branch. However, as our team has updated the project’s documentation, we noticed that these updates were not showing on the WorldWind website. WorldWind’s open-source nature means the source code (even from develop) can be used by developers at anytime, and we want to keep the website documentation up-to-date with whatever the WorldWind team is currently working on.

For releases, any release branch we create will be merged into develop once the release is official, thereby keeping all documentation up-to-date. The documentation for official releases will always be available, however only through the release packages.