Document all member-record-sub functions.

MODULES.md

@@ -98,7 +98,7 @@ Known types are:
 
 The structure is perfectly suited for ```print-source-listing``` function.
 
-    (member-sub-ref mr sec key [default])
+    (member-record-sub-ref mr sec key [default])
 
 * ```mr``` - a member record structure
 * ```sec``` - section symbol
@@ -109,7 +109,7 @@ Retrieves given ```key``` from dictionary stored as section ```sec```
 in given ```mr``` structure. If no ```default``` is provided and the
 ```key``` does not exist it raises an exception.
 
-    (member-sub-set mr sec key value)
+    (member-record-sub-set mr sec key value)
 
 * ```mr``` - a member record structure
 * ```sec``` - section symbol
@@ -120,6 +120,36 @@ Sets the value of given ```key``` in dictionary stored as section
 ```sec``` in given ```mr``` structure to the new ```value``` possibly
 overwriting previous one.
 
+    (member-record-sub-prepend mr sec key value)
+
+* ```mr``` - a member record structure
+* ```sec``` - section symbol
+* ```key``` - key symbol
+* ```value``` - value to prepend (cons) to the key current value
+
+Prepends (cons) new the ```value``` to current value of given ```key``` in
+dictionary stored as section ```sec``` in given ```mr``` structure
+replacing the original value.
+
+    (member-record-sub-has-key? mr sec key)
+
+* ```mr``` - a member record structure
+* ```sec``` - section symbol
+* ```key``` - key symbol
+
+Returns ```#t``` if given section ```sec``` contains the ```key```.
+
+    (member-record-sub-ensure mr sec key value)
+
+* ```mr``` - a member record structure
+* ```sec``` - section symbol
+* ```key``` - key symbol
+* ```value``` - value to set
+
+Sets the value of given ```key``` in dictionary stored as section
+```sec``` in given ```mr``` structure to the new ```value``` if and
+only if it is not already present.
+
 ### Member Parser
 
 ### Members Directory