Dealloc crash fix for observation

[BrianDoig]

• (void)removeObserverForKeyPath:(NSString *)inKeyPath identifier:(NSString *)token;
• (void)removeAllBlockObservers;

These two methods could crash because dealloc calls free as soon as it exits. The dispatch_asynch could cause the removal of the observer after free has occurred.

• (NSString *)addObserverForKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options task:(BKObservationBlock)task;
• (void)addObserverForKeyPath:(NSString *)keyPath identifier:(NSString *)token options:(NSKeyValueObservingOptions)options task:(BKObservationBlock)task;

These two methods were added so that you can create a observer that requires one of the options to function properly.

[zwaldowski]

This and some other changes will be rolled into 0.9.5 shortly. Huge thanks for your support!