Marshal GVAlues that hold a Float value

Change-Id: Iba6bdcf2c9e27a487dfc70892f1069f4643c41f5
Allow to encode/decode NULL strings

Change-Id: Ife04b6ab50a2e153087a57a01e6b7c0a31898c84
Marshal GVAlues that hold a STRING value

Change-Id: Id2bb6cce0ba538f8264081eb74fdbbca11796aba
format source code

Change-Id: Ic83fdf1ba9ec87b8fcfde124b3444ee77610ce6f