New Build System

[Craig Cavanaugh]

I am switching jGnash over to use Gradle as the build system.  For the most part, it's behaving well, but there is always opportunity for breakage.  I'm finding the (re)build process is much faster with Gradle.

Gradle pros are more than welcome to help improve the setup.

The most significant change is the resultant application executable are a bit different. Exe files are still provided and executable Bash scripts are for Unix based systems is included.

The gradle wrapper is being used, so there is no need to install Gradle.  The README.adoc details the build process and changes.

Thanks,

Craig