sdbm-hash algorithm

I added the sdbm hash algorithm

snippets/sdbm_hash.md

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+
+This function implements the **sdbm** hash-algorithm. 
+It uses the charCodeAt-methode and the shift-operator.
+
+``` js
+function sdbm(s) {
+    var hashCode = new Number();
+    for (var i = 0; i < s.length; i++) {
+        hashCode = s.charCodeAt(i) + (hashCode << 6) + (hashCode << 16) - hashCode;
+    }
+    return hashCode;
+}
+```