Publish bifurcated artifacts to support both Java 7 and Java 8

In this release, I finally brought support for Java 7 up to the same level as that offered for Java 8. To facilitate this support, I added a Gradle project to build and publish two separate artifacts. I also updated the existing Maven project to facilitate building these artifact variants locally.

The feature set of the newly published Java 7 artifact hasn't changed, but its dependencies have been updated to pull in fixes for security defects in these dependencies.