Meaningful Changes

Fix a bug where setting a property inside of a notification event listener and break the guarantee that clients should be ready before host side effects are processed
Split _flushProperties into two functions
- _enableProperties to set up property accessors on an element
- _flushProperties now only handles batching changed properties to effects like observers
- Neither function should need to be called by user code, but exist as override points for databinding

Raw Notes

[skip ci] doc fixes (commit)
Docs and slight renaming. (commit)
Add tests. (commit)
Move hostStack to property-effects and make readyClients explicit (commit)
Turn on accessors (via __dataInitialized) only after clients have completely flushed. (commit)
Adds _enableProperties as a new entry point that must be called to turn on properties. Prevents a bug where _readyClients can be called twice. (commit)
[ci skip] Fix doc createPropertyEffect -> addPropertyEffect (commit)
[ci skip] Update Changelog (commit)