DecisionTreeClassifier can not be used with String classes

When experimenting with [RandomTreeForests](http://scikit-learn.org/stable/modules/ensemble.html#forests-of-randomized-trees) I noticed that they could not work on our input data.

Also the documentation for the [DecisionTreeClassifier.fit(X,y)](http://scikit-learn.org/stable/modules/generated/sklearn.tree.DecisionTreeClassifier.html#sklearn.tree.DecisionTreeClassifier.fit) states for the class parameter `y`

> The target values (integers that correspond to classes in classification, real numbers in regression).

So I ran the classifier again with integer classes instead of characters and the success rate of the tree dramatically improved:

Old:
```
Using Dataset Out of the Box Integer Data :
    Training Decision Tree Classifier:
        Training in 0 Seconds
        Prediction in 0 Seconds
        2680 errors out of 4000 validation vectors
 
Using Dataset Normalizerd Float Data :
    Training Decision Tree Classifier:
        Training in 0 Seconds
        Prediction in 0 Seconds
        2679 errors out of 4000 validation vectors
```

New:
```
Using Dataset Out of the Box Integer Data :
    Training Decision Tree Classifier:
        Training in 0 Seconds
        Prediction in 0 Seconds
        518 errors out of 4000 validation vectors
 
Using Dataset Normalizerd Float Data :
    Training Decision Tree Classifier:
        Training in 0 Seconds
        Prediction in 0 Seconds
        512 errors out of 4000 validation vectors
```