Convert nng_random to new format.

docs/ref/SUMMARY.md

@@ -3,11 +3,15 @@
 - [API](./api.md)
 
   - [Threading Functions](./api/thr/index.md)
+
     - [nng_mtx](./api/thr/nng_mtx.md)
+
   - [Utility Functions](./api/util/index.md)
+
     - [nng_clock](./api/util/nng_clock.md)
     - [nng_id_map](./api/util/nng_id_map.md)
     - [nng_msleep](./api/util/nng_msleep.md)
+    - [nng_random](./api/util/nng_random.md)
 
 - [Transports](./tran/index.md)
 

docs/ref/api/util/index.md

@@ -1,5 +1,11 @@
 # Utility Functions
 
+This section documents various utility functions that may help
+with application portability. These are not fundamental to NNG
+or Scalability Protocols, but we find them useful for a variety
+of other uses.
+
 - [nng_clock](nng_clock.md)
 - [nng_id_map](nng_id_map.md)
 - [nng_msleep](nng_msleep.md)
+- [nng_random](nng_random.md)

docs/ref/api/util/nng_random.md

@@ -0,0 +1,25 @@
+# nng_random
+
+## NAME
+
+nng_random --- get random number
+
+## SYNOPSIS
+
+```c
+#include <nng/nng.h>
+
+uint32_t nng_random(void);
+```
+
+## DESCRIPTION
+
+The `nng_random` returns a random number.
+The value returned is suitable for use with cryptographic functions such as
+key generation.
+The value is obtained using platform-specific cryptographically strong random
+number facilities when available.
+
+## RETURN VALUES
+
+Returns a random 32-bit value.