Scripting API and Custom Effects via C - v1.2.9

PLEASE ALWAYS BACKUP YOUR PROJECTS BEFORE UPDATING.

(A guide on how to update to new versions is available in the documentation.)

## Scripting API and Custom Effects via C ##
- Added: Scripting API sections in the documentation, automatically built from code.
- Added: “Behavior Effects Fallbacks”, which let you set which behavior effects to apply to a text/letter if it has no other tags assigned.
- Improved: Custom Effects C# classes are automatically recognized.
- Improved: comments in all public APIs, also expanded with examples and manual references.
- Bugfix: effect classes are not stripped from the build for AOT platforms (or IL2CPP).
- General: various performance improvements and bugfixes

Full changelog in the documentation.