Update README.md & version bump

Tested with 2.0.0-beta from NuGet & things seem fine.
Removing beta status.

Support for validate value callback (#17) (#20)

* added support for validation (#17)
* added more generated dox - documentation for "Gen" methods has info about associated methods/events for validation, coercion, & changes
* updated readme with details about validation
* unrelated maintenance in tests

fix for #18 - generated documentation has been added to properties & …

…events (#19)

* added default documentation comments
dependency & attached properties now get default-generated dox comments so the compiler doesn't complain

updated documentation comments (#16)

This fixes #15 where type names of constructed generic types were causing warnings when documentation files are generated for a project

Generated change-handlers can use routed events (#14)

If we find a routed event that appears to match the dependency property, then it may be used as the property-changed handler.

In the case of multiple candidates, the priority is
- static methods
- instance methods
- routed events

Implemented generator for Routed events (#12)

* implemented generator for routed events

* updated all sorts of unit tests

note:
Weird issue seen when debugging `GenEvents` test with "RoutedEvent2.cs":
We end up with 2 different `System.MulticastDelegate` type symbols (they're coming from different assemblies (fishy business with dynamic compilation + source gen?)).
This makes a comparison fail & we produce the wrong handler type.
This issue does not happen under normal usage & other, real unit tests so I'm not too worried about it.

* update README.md

* refactored diagnostics code

improved formatting of generated code (#10)

saw this style [https://github.com/maryamariyan/runtime/blob/2814f8912c05019c1d1b161e0201eda3f7fc8e69/src/libraries/Microsoft.Extensions.Logging.Abstractions/gen/LoggerMessageGenerator.Emitter.cs](here) & thought it was good

makes things nicer with more line breaks & uses `Append` instead of `AppendLine`, which has better performance

Code cleanup (#9)

* minor cleanup

- corrected some comments
- updated gen code formatting (added some indentation)
- change `ApppendPropertyMetadata` to `GetPropertyMetadataDeclaration`
- check cancellation during code gen
- added param names for clarity

* more unit tests

added support for `FrameworkPropertyMetadataOptions` (#7)

* added support for `FrameworkPropertyMetadataOptions` (#6)
* updated comments / documentation
* misc cleanup