Prepare for 2.x interface.

Changes:
* Adding `??attr` binding syntax.
* Changing `ifDefined` to delete attr on `null` as well as `undefined`.
* Deprecating `ifDefined` / `nullish` in favor of `??attr` binding.
* Deprecating `repeat` in favor of `map`.
* Updating documentation.

Closes #204.

CHANGELOG.md

@@ -6,10 +6,34 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- You can now bind attributes with `??foo="${bar}"` syntax. This is functionally
+  equivalent to the `nullish` updater and will replace that functionality later.
+- A new `unsafe` updater was added to replace `unsafeHTML` and `unsafeSVG`. You
+  use it like `unsafe(value, 'html')` and `unsafe(value, 'svg')`.
+
 ### Changed
 
 - Template errors now include approximate line numbers from the offending
   template. They also print the registered custom element tag name (#201).
+- The `ifDefined` updater now deletes the attribute on `null` in addition to
+  `undefined`. This makes it behave identically to `nullish`. However, both
+  updaters are deprecated and the `??attr` binding should be used instead.
+
+### Deprecated
+
+- The `ifDefined` and `nullish` updaters are deprecated, update templates to use
+  syntax like `??foo="${bar}"`.
+- The `repeat` updater is deprecated, use `map` instead.
+- The `unsafeHTML` and `unsafeSVG` updaters are deprecated, use `unsafe`.
+
+### Fixed
+
+- Transitions from different content values should all now work. For example,
+  you previously could not change from a text value to an array. Additionally,
+  state is properly cleared when going from one value type to another — e.g.,
+  when going from `unsafe` back to `null`.
 
 ## [1.1.1] - 2024-11-09
 
@@ -27,20 +51,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - New support for static `styles` getter for `adoptedStyleSheets` ergonomics
   (#52).
 
-### Fixed
-
-- The `map` function now works with properties / attributes bound across
-  template contexts (#179).
-- The `x-element.d.ts` file now reflects the actual interface. Previously, it
-  has some issues (e.g., improper module export).
-
 ### Changed
 
 - The `x-element.js` file is now “typed” via JSDoc. The validity of the JSDoc
   comments are linted alongside the rest of the code and the annotations there
   are exported into a generated `x-element.d.ts` file. Previously, that file was
   hand-curated.
 
+### Fixed
+
+- The `map` function now works with properties / attributes bound across
+  template contexts (#179).
+- The `x-element.d.ts` file now reflects the actual interface. Previously, it
+  has some issues (e.g., improper module export).
+
 ## [1.0.0] - 2024-02-29
 
 ### Added