v0.3.0

• Image and Component: Remove transformation properties, leave as plain attribute.
• Use fontTools.misc.transform.Transform instead of our own Transformation
• Image.transformation and Component.transformation default to fontTools.misc.transform.Identity().
• Contour now behaves like a collections.abc.MutableSequence. append(), clear(), remove() and reverse() should now be done on the actual points.
• Info: all attributes are now optional, avoiding writing empty lists to fontinfo.plist.
• LayerSet: load layers on iteration.
• Font.guidelines returns [] if Info.guidelines is None. This allows to blindly iterate over Font.guidelines.
• DataStore.write(): Data is now actually retained in-memory before the reader is deleted when saving as. Before, data that had not been accessed was written to disk but not formally loaded into DataStore.data