fix: add lowercase property aliases for button-element

Provides support for svelte properties.

This change also includes examples for svelte.

examples/svelte/.gitignore

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+/node_modules/
+/public/build/
+
+.DS_Store

examples/svelte/.vscode/extensions.json

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+{
+  "recommendations": ["svelte.svelte-vscode"]
+}

examples/svelte/README.md

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+_Looking for a shareable component template? Go here -->
+[sveltejs/component-template](https://github.com/sveltejs/component-template)_
+
+---
+
+# svelte app
+
+This is a project template for [Svelte](https://svelte.dev) apps. It lives at https://github.com/sveltejs/template.
+
+To create a new project based on this template using [degit](https://github.com/Rich-Harris/degit):
+
+```bash
+npx degit sveltejs/template svelte-app
+cd svelte-app
+```
+
+_Note that you will need to have [Node.js](https://nodejs.org) installed._
+
+## Get started
+
+Install the dependencies...
+
+```bash
+cd svelte-app
+npm install
+```
+
+...then start [Rollup](https://rollupjs.org):
+
+```bash
+npm run dev
+```
+
+Navigate to [localhost:5000](http://localhost:5000). You should see your app running. Edit a component file in `src`,
+save it, and reload the page to see your changes.
+
+By default, the server will only respond to requests from localhost. To allow connections from other computers, edit the
+`sirv` commands in package.json to include the option `--host 0.0.0.0`.
+
+## Building and running in production mode
+
+To create an optimised version of the app:
+
+```bash
+npm run build
+```
+
+You can run the newly built app with `npm run start`. This uses [sirv](https://github.com/lukeed/sirv), which is
+included in your package.json's `dependencies` so that the app will work when you deploy to platforms like
+[Heroku](https://heroku.com).
+
+## Single-page app mode
+
+By default, sirv will only respond to requests that match files in `public`. This is to maximise compatibility with
+static fileservers, allowing you to deploy your app anywhere.
+
+If you're building a single-page app (SPA) with multiple routes, sirv needs to be able to respond to requests for _any_
+path. You can make it so by editing the `"start"` command in package.json:
+
+```js
+"start": "sirv public --single"
+```
+
+## Using TypeScript
+
+This template comes with a script to set up a TypeScript development environment, you can run it immediately after
+cloning the template with:
+
+```bash
+node scripts/setupTypeScript.js
+```
+
+Or remove the script via:
+
+```bash
+rm scripts/setupTypeScript.js
+```
+
+## Deploying to the web
+
+### With [Vercel](https://vercel.com)
+
+Install `vercel` if you haven't already:
+
+```bash
+npm install -g vercel
+```
+
+Then, from within your project folder:
+
+```bash
+cd public
+vercel deploy --name my-project
+```
+
+### With [surge](https://surge.sh/)
+
+Install `surge` if you haven't already:
+
+```bash
+npm install -g surge
+```
+
+Then, from within your project folder:
+
+```bash
+npm run build
+surge public my-project.surge.sh
+```