Update Windows build files to Visual Studio 2015, add x64 platform, and adjust for libsrtp 2.0.x changes.

(These project files should work on older Visual Studio versions back to Visual Studio 2010 with minor adjustments.)
diff --git a/config.hw b/config.hw
index 39d4e07..135cccf 100644
--- a/config.hw
+++ b/config.hw
@@ -3,6 +3,7 @@
 
 #if (_MSC_VER >= 1400)
 # define HAVE_RAND_S	1
+# define _CRT_RAND_S
 #endif
 
 /* Define if building for a CISC machine (e.g. Intel). */
@@ -11,9 +12,6 @@
 /* Define if building for a RISC machine (assume slow byte access). */
 /* #undef CPU_RISC */
 
-/* Path to random device */
-/* #define DEV_URANDOM "/dev/urandom" */
-
 /* Define to compile in dynamic debugging system. */
 #define ENABLE_DEBUGGING 1