Improve documentation of json parser functions

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

include/mysql/service_json.h

@@ -20,23 +20,25 @@
   @file
   json service
 
-  Esports JSON parsing methods for plugins to use.
+  Exports JSON parsing methods for plugins to use.
 
-  Fuctions of the service:
-    js_type - returns the type of the JSON argument,
+  Functions of the service:
+    json_type - returns the type of the JSON argument,
        and the parsed value if it's scalar (not object or array)
 
-    js_get_array_item - expecs JSON array as an argument,
-       and returns the n_item's item's type and value
+    json_get_array_item - expects JSON array as an argument,
+       and returns the type of the element at index `n_item`.
        Returns JSV_NOTHING type if the array is shorter
-       than n_item and the actual length of the array in v_len.
+       than n_item and the actual length of the array in value_len.
+       If successful, then `value` up till `value[value_len]` contains the array
+       element at the desired index (n_item).
 
-    js_get_object_key - expects JSON object as an argument,
-       searches for a key in the object, return it's type and value.
+    json_get_object_key - expects JSON object as an argument,
+       searches for a key in the object, return it's type and stores its value in `value`.
        JSV_NOTHING if no such key found, the number of keys
        in v_len.
 
-    js_get_object_nkey - expects JSON object as an argument.
+    json_get_object_nkey - expects JSON object as an argument.
       finds n_key's key in the object, returns it's name, type and value.
       JSV_NOTHING if object has less keys than n_key.
 */