Added tags to ipython notebooks to find previous algorithms.

ipython/EulerProblem004.ipynb

@@ -53,7 +53,9 @@
   {
    "cell_type": "code",
    "execution_count": 2,
-   "metadata": {},
+   "metadata": {
+    "collapsed": false
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -78,7 +80,9 @@
   {
    "cell_type": "code",
    "execution_count": 4,
-   "metadata": {},
+   "metadata": {
+    "collapsed": false
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -115,7 +119,9 @@
   {
    "cell_type": "code",
    "execution_count": 5,
-   "metadata": {},
+   "metadata": {
+    "collapsed": false
+   },
    "outputs": [
     {
      "name": "stdout",
@@ -159,8 +165,12 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.3"
-  }
+   "version": "3.5.4"
+  },
+  "tags": [
+   "palindrome",
+   "combinations"
+  ]
  },
  "nbformat": 4,
  "nbformat_minor": 2