fixes to simple inventory

fixes #19
fixes #18

- Adds the inventory methods inv#isEmpty() and inv#count().
- Fixes minor inconsistency with inv#pickUp() and <<pickup>> macro behavior when used with unique keyword.

docs/simple-inventory.md

@@ -470,7 +470,7 @@ This method is useful for enforcing uniqueness; that is, preventing doubles or d
 
 Instance methods, unlike static methods, are called directly on the inventory object, so you replace `<inventory>` with the variable you're using to store / reference the inventory instance you want to work on.  See the examples for the methods below if that confuses you.
 
-Of particular note to authors: `<inventory>.has()`, `<inventory>.hasAll()`, and `<inventory>.toArray()`
+Of particular note to authors: `<inventory>.has()`, `<inventory>.hasAll()`, `<inventory>.toArray()`, `<inventory>.count()`, and `<inventory>.isEmpty()`.
 
 ##### `<inventory>.pickUp()`
 
@@ -634,6 +634,46 @@ This method returns an array made up of the items in the calling inventory.  Use
 <<= _items.join(', ')>> /% shows 'uh oh' %/
 ```
 
+##### `<inventory>.count()`
+
+**Return Value**: Integer.
+
+**Syntax**: `<inventory>.count([item])`
+
+This method returns the total number of items in the inventory. If you pass it a string corresponding to an item name, it will instead check for how many duplicates of that item are in the inventory.
+
+**Arguments**:
+
+* **item**: (optional) the item to count duplicates of.
+
+**Usage**:
+```
+/% create an array based on the inventory %/
+<<newinventory '$inv' 'this' 'that' 'the other' 'another' 'that'>>
+
+<<= $inv.count()>> /% 5 %/
+<<= $inv.count('this')>> /% 1 %/
+<<= $inv.count('that')>> /% 2 %/
+```
+
+##### `<inventory>.isEmpty()`
+
+**Return Value**: Boolean.
+
+**Syntax**: `<inventory>.isEmpty()`
+
+This method returns whether or not the inventory is empty (has zero items in it). You can also compare `<inventory>.count()` to `0` to achieve similar results.
+
+**Usage**:
+```
+/% check if the inventory is empty %/
+<<if $inventory.isEmpty()>>
+    You aren't carrying anything.
+<<else>>
+    You have some things on you.
+<</if>>
+```
+
 ##### `<inventory>.sort()`
 
 **Return Value**: This inventory (chainable).

scripts/simple-inventory.js

@@ -1,5 +1,5 @@
 // simple-inventory.js, by chapel; for sugarcube 2
-// version 2.1.0
+// version 2.2.0
 
 // namespace
 setup.simpleInv = {};
@@ -140,12 +140,12 @@ setup.simpleInv.inventory.prototype = {
     pickUp : function (unique) { // add items to this inventory
         var items = [].slice.call(arguments).flatten(), inventory = this;
         if (items && items.length) {
-            if (unique === 'unique' || items[0] === 'unique') { // JS API only; items must be unique in eash inventory instance
+            if (unique === 'unique' || items[0] === 'unique') { // items must be unique in each inventory instance
                 items = items.splice(1);
                 items = (function (items) { 
                     var ret = []; // this code could use some cleanup
                     items.forEach(function (item) {
-                        if (!inventory.inv.includes(item)) {
+                        if (!inventory.inv.includes(item) && !ret.includes(item)) {
                             ret.push(item);
                         }
                     });
@@ -203,6 +203,25 @@ setup.simpleInv.inventory.prototype = {
     toArray : function () { // not super necessary
         return (this.inv);
     },
+
+    count : function (item) {
+        // if item, count the number of duplicates
+        if (item && typeof item === 'string') {
+            var cnt = 0;
+            this.toArray().forEach( function (i) {
+                if (i === item) {
+                    cnt++;
+                }
+            });
+            return cnt;
+        }
+        // else return the length
+        return this.toArray().length;
+    },
+
+    isEmpty : function () {
+        return this.toArray().length === 0;
+    },
 
     linkedList : function (loc, action) { // construct the list elements to keep the macro call clean-ish
         if (!loc || !(loc instanceof setup.simpleInv.inventory)) {
@@ -301,7 +320,7 @@ if (setup.simpleInv.options.tryGlobal) {
 Macro.add('newinventory', {
     handler : function () {
 
-        if (this.args.length !== 1) {
+        if (this.args.length < 1) {
             return this.error('incorrect number of arguments');
         }
         var varName = this.args[0].trim();