JNI: Initial commit of C wrapper functions

If the user runs "configure --enable-java", a separate library is built
with Java native interface stubs and it can be loaded with:

    System.loadLibrary("openconnect-wrapper");

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
JNI: Initial commit of Java library + example program

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
main: Add openconnect_vpninfo_free() on a couple of exit paths

This makes it easier to check for library memory leaks.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>