Ensure that a reference to underscore exists in _.mask (??).
Migrate to Backbone 0.9.10 and add generic storage

Moving to a more generalized storage mechanism (L.store instead of
assuming localStorage) will make porting to various platforms easier.
This new storage system is also asynchronous (faster but introduces
complexity). The API of L.store is as follows:

    L.store.get(key, {success: function(val) {...}, error: function(e) {...}})
    L.store.set(key, val, {success: function() {...}, error: function(e) {...}})
    L.store.remove(key, {success: function() {...}, error: function(e) {...})
    L.store.clear({success: function() {...}, error: function(e) {...})
Manage localStorage better.
Begin working on firefox support (broken).