Deep Observe

[Waidhoferj]

Fixes #43
Added deep observe option to all YTypes

Example

# will observe mutations directly on the `YArray` (old api)
sub = y_array.observe(fn)

# will recursively observe events inside the `YArray`
sub = y_array.observe(fn, deep=True)

Updates

• Added documentation and test cases.
• Implemented deep observe for YText, YMap, YArray, YXmlElement, and YXmlText.
• Fixed issue where deep observers will not unsubscribe.
• Tested YText deep observe with embedded objects (requires Added rich text formatting #21)

[Horusiath]

I'm not sure if using deep=True argument is desirable, as observe and observe_deep put different type signatures for subscriber callbacks in Yrs. observe uses a specific event per Y type. observe_deep is more generic and it's subscriber takes a list of events "bubbling up" from children Y types instead.

[Waidhoferj]

Additions

• New trait DefaultPyErr to create centralized default error messages for custom Ypy exceptions
• SubscriptionIds now obscure their contents in two classes: DeepSubscription and ShallowSubscription
• unobserve now handles both deep and shallow subscriptions
• Integrated rich text for YText