give users module proper usage info, subsequently fix empty params erroring

modules/users/commands.js

@@ -97,6 +97,10 @@ var commands = function(dbot) {
         } 
     };
     
+    commands['~alias'].regex = [/^~alias ([\d\w[\]{}^|\\`_-]+?)/, 2];
+    commands['~setaliasparent'].regex = [/^~setaliasparent ([\d\w[\]{}^|\\`_-]+?)/, 2];
+    commands['~mergeusers'].regex = [/^~mergeusers ([\d\w[\]{}^|\\`_-]+?)\s*?([\d\w[\]{}^|\\`_-]+?)/, 3];
+    
     commands['~setaliasparent'].access = 'moderator';
     commands['~mergeusers'].access = 'moderator';
     

modules/users/usage.json

@@ -0,0 +1,5 @@
+{
+    "~alias": "~alias [nick]",
+    "~setaliasparent": "~setaliasparent [nick]",
+    "~mergeusers": "~mergeusers [primary] [secondary]"
+}