Refactor repository. Fixes #2161 (#2192)

* Remove duplicate LICENSE.
* Remove un-userd pyscript.sw directory and its content.
* Remove ReadTheDocs settings (unused).
* Remove un-used pyproject.toml
* Remove now unused CHANGELOG. Changes now tracked via release notes on GitHub.
* Updated / cleaned release page template and associated GH actions.
* Update prettierignore to remove un-needed refs.
* Move troubleshooting into correct README.
* Add reason for the index.html
* Rename the "pyscript.core" directory to "core".
* Update PR template because CHANGELOG is no longer used.
* Codespell configuration in pyproject.toml.
* Update pyscript.core -> core in .githubignore
* Remove test-results/.last-run.json. This should be ignored by git.
* Pin nodejs version.

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

core/src/plugins/error.js

@@ -0,0 +1,47 @@
+// PyScript Error Plugin
+import { hooks } from "../core.js";
+
+hooks.main.onReady.add(function override(pyScript) {
+    // be sure this override happens only once
+    hooks.main.onReady.delete(override);
+
+    // trap generic `stderr` to propagate to it regardless
+    const { stderr } = pyScript.io;
+
+    // override it with our own logic
+    pyScript.io.stderr = (error, ...rest) => {
+        notify(error.message || error);
+        // let other plugins or stderr hook, if any, do the rest
+        return stderr(error, ...rest);
+    };
+
+    // be sure uncaught Python errors are also visible
+    addEventListener("error", ({ message }) => {
+        if (message.startsWith("Uncaught PythonError")) notify(message);
+    });
+});
+
+// Error hook utilities
+
+// Custom function to show notifications
+
+/**
+ * Add a banner to the top of the page, notifying the user of an error
+ * @param {string} message
+ */
+export function notify(message) {
+    const div = document.createElement("div");
+    div.className = "py-error";
+    div.textContent = message;
+    div.style.cssText = `
+    border: 1px solid red;
+    background: #ffdddd;
+    color: black;
+    font-family: courier, monospace;
+    white-space: pre;
+    overflow-x: auto;
+    padding: 8px;
+    margin-top: 8px;
+  `;
+    document.body.append(div);
+}