Add function to return library version at execute time. Fix Issue 39. Thanks to Zuck for his contribution.

Remove compilation warning due to missing includes in examples.

src/examples/nfc-mfclassic.c

@@ -31,7 +31,9 @@
 #include <ctype.h>
 
 #include "libnfc.h"
+
 #include "mifaretag.h"
+#include "bitutils.h"
 
 static dev_info* pdi;
 static tag_info ti;