New: interpolations as functions within elements content

This aligns uhtml with lighterhtml and hyperHTML, so that whenever an interpolation is a callback, it'll be invoked right away, passing along the node.

This new feature enables plugins and extensions to what uhtml offers already, beside making it identical, in behavior, to lighterhtml.

DOCUMENTATION.md

@@ -432,14 +432,15 @@ render(document.body, html`
 
 Beside nodes where the content will be inevitably just text, like it is for `style` or `textarea`, as example, every other interpolation can contain primitives, as strings, numbers, or even booleans, or the returned value of `html` or `svg`, plus regular DOM nodes.
 
-The only special case are _Array_ of either primitives, or returned values from `html` or `svg`.
+The only special case are _Array_ of either primitives, or returned values from `html` or `svg`, and since *2.5* _Function_, invoked and resolved after invoke.
 
 
 ```js
 render(document.body, html`
   <ul>
     <li>This is ${'primitive'}</li>
     <li>This is joined as primitives: ${[1, 2, 3]}</li>
+    <li>This is a callback: ${utility}</li>
     ${lines.map((text, i) => html`
       <li>Row ${i} with content: ${text}</li>
     `)}

README.md

@@ -14,6 +14,10 @@ Please ask questions in the [dedicated discussions repository](https://github.co
 
 ---
 
+### V2.5 Update
+
+  * an interpolated value, within a *DOM* element, can now be a `function`, enabling a world of *µhtml* extending possibilities, also aligning the behavior with both *lighterhtml* and *hyperHTML*. That is: `<el>${callback}</el>`! The `callback` will be invoked with the *comment* pin/placeholder as unique argument, where its `parentNode` would be the element containing such comment, if needed, and its returned value will be passed along the same mechanism that resolves already all other cases.
+
 ### V2.4 Update
 
   * a new `?attribute=${value}` prefix, with a question mark, has landed, after [this long debate](https://github.com/WebReflection/discussions/discussions/13), and based to the fact *µhtml* never wants to be ambiguous. However, the mighty [lit-html](https://terodox.tech/lit-html-part-2/) put an end to the debate, disambiguating through a `?` question mark prefix, which explicits developers intents, and works well across browsers. So that's it: whenever you expect an attribute to be in, or out, use `?name=${value}` and win the day 🥳

cjs/handlers.js

@@ -51,6 +51,9 @@ const handleAnything = comment => {
           nodes = diff(comment, nodes, [text]);
         }
         break;
+      case 'function':
+        anyContent(newValue(node));
+        break;
       // null, and undefined are used to cleanup previous content
       case 'object':
       case 'undefined':