Font mapping legend
Hi there,

I've recently used your library in my app but have an issue which I hope you can clarify. A disclaimer: I'm a beginner at Android programming. I've attached a screenshot to show you exactly what happens.

I have two icons next to each other in an XML as so:

``` xml
<com.mikepenz.iconics.view.IconicsButton
                    android:id="@+id/button_share"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:layout_centerVertical="true"
                    android:layout_toLeftOf="@+id/button_star"
                    android:background="?attr/selectableItemBackgroundBorderless"
                    android:text="{gmd-favorite-outline}"
                    android:textColor="@color/primary_dark_material_light"
                    android:textSize="24sp" />

<com.mikepenz.iconics.view.IconicsButton
                    android:id="@+id/button_star"
                    android:layout_width="48dp"
                    android:layout_height="48dp"
                    android:layout_alignParentRight="true"
                    android:layout_centerVertical="true"
                    android:background="?attr/selectableItemBackgroundBorderless"
                    android:text="{faw-star-o}"
                    android:textColor="@color/primary_dark_material_light"
                    android:textSize="24sp" />
```

The button using Font Awesome renders perfectly but the button using GMD just shows me the text. What am I doing wrong?

Here is the screenshot:
![gmd](https://cloud.githubusercontent.com/assets/3102714/8865165/b3b51f18-31dd-11e5-835d-9bd4306406a4.png)

Can the legend for the different fonts be added to the README as well?
