Add invalidateCache() method for cache invalidation

Fixes Gottox#17

README.md

@@ -28,4 +28,15 @@ For enabling this cache in your query just call .cache()
 db.User.find({ ... }).cache().exec(function() { ... })
 ```
 
+To invalidate the cache for a query, just call invalidateCache()
+```javascript
+db.User.find({ ... }).invalidateCache().exec(function() { ... })
+```
+This will clear the current query from the cache, other queries may remain
+in the cache, nevertheless. If you want to clear/reset the whole cache, run
+invalidateCache(true) on Query
+```javascript
+db.User.find({ ... }).invalidateCache(true).exec(function() { ... })
+```
+
 For more talky output add ```debug: true``` to the cacheOpts.

lib/cache.js

@@ -14,6 +14,21 @@ exports.install = module.exports.install = function(mongoose, options, Aggregate
 		return this;
 	};
 
+	mongoose.Query.prototype.invalidateCache = function(resetGlobal) {
+		var key = genKey(this);
+
+		if (resetGlobal) {
+			cache.reset();
+			return this;
+		}
+		if (!cache.has(key)) {
+			log('Requested cache invalidation, but this isn\'t cached.');
+			return this;
+		}
+		cache.del(key);
+		return this;
+	};
+
 	if (typeof Aggregate !== 'undefined') {
 		orig.execAggregate = Aggregate.prototype.exec;
 		Aggregate.prototype.cache = function() {