cleanup library and some basic tests. Includes, add guards to includes
diff --git a/include/polarssl/net.h b/include/polarssl/net.h
index d86732f..5f0b9ca 100644
--- a/include/polarssl/net.h
+++ b/include/polarssl/net.h
@@ -24,7 +24,7 @@
 #ifndef POLARSSL_NET_H
 #define POLARSSL_NET_H
 
-#include <string.h>
+#include <stddef.h>
 
 #define POLARSSL_ERR_NET_UNKNOWN_HOST                      -0x0056  /**< Failed to get an IP address for the given hostname. */
 #define POLARSSL_ERR_NET_SOCKET_FAILED                     -0x0042  /**< Failed to open a socket. */