Initial commit of ribbit library

Zero-dependency WYSIWYG markdown editor for the browser, extracted
from the ttfrog wiki engine. Initial commit.

README.md

@@ -1,3 +1,44 @@
 # ribbit
 
-Dependency-free WYSIWYG markdown/html editor
+Zero-dependency WYSIWYG markdown editor
+
+## Files
+
+- `src/hopdown.js` — Markdown ↔ HTML converter (`HopDown.toHTML()`, `HopDown.toMarkdown()`)
+- `src/ribbit.js` — Base viewer class (`Ribbit`), plugin base class (`RibbitPlugin`), utilities
+- `src/ribbit-editor.js` — Editor class (`RibbitEditor`) with VIEW/EDIT/WYSIWYG modes
+- `src/ribbit.css` — Editor and content styles
+
+## Usage
+
+```html
+<link rel="stylesheet" href="ribbit/src/ribbit.css">
+<article id="ribbit">your markdown here</article>
+
+<script src="ribbit/src/hopdown.js"></script>
+<script src="ribbit/src/ribbit.js"></script>
+<script src="ribbit/src/ribbit-editor.js"></script>
+<script>
+    const editor = new RibbitEditor({ plugins: [] });
+    editor.run();
+
+    // Switch modes
+    editor.wysiwyg();  // WYSIWYG editing
+    editor.edit();      // Source editing
+    editor.view();      // Read-only view
+
+    // Get content
+    editor.getMarkdown();
+    editor.getHTML();
+</script>
+```
+
+## Supported Markdown
+
+Bold, italic, inline code, links, headings (h1-h6), unordered/ordered/nested lists,
+blockquotes, fenced code blocks with language, horizontal rules, GFM tables with
+column alignment, and paragraphs. Arbitrary nesting of all inline formatting.
+
+## Tests
+
+Open `test/test_ribbit-down.html` in a browser.