Upgraded jna to 3.5.2 and switched to Gradle

I've just switched to Gradle as I'd like to start adding some tests to the library.

I wasn't sure which version of JNA was being used so I grabbed latest and fixed the issues I found.

The issues were to do with the absence of getFieldOrder(). I believe the introduction of getFieldOrder() in JNA is for Java 7 compatibility.

I was able to mount both of the examples on OSX with osxfuse.