Require Java 1.6 again (not 1.7) (#17).

I erroneously pushed 0.2.1 that broke backwards compatibility with users of JDK 1.6 which was all 0.2.0 required. Also, it is unlikely that anyone is using the AutoCloseable interface, as it requires a cast. Therefore, this change returns to JDK 1.6 compatibility.
[release] Release jnasmartcardio-0.2.2.
[release] Change development version to 0.2.3-SHAPSHOT.