Create book and deploy it to the website (#6)

* Create book structure.
* Add workflow for linting the markdown using markdownlint.
* Add workflow for building the book with mdBook and deploying to the website.
* Restyle mdBook and support GitHub-style alerts.
* Add images zooming.
* Add index, firmware structure and gyroscope articles.

docs/js.js

@@ -0,0 +1,7 @@
+// Enable zoom on images larger than 300px
+document.querySelectorAll('.content img').forEach(function (img) {
+	var width = img.getAttribute('width');
+	if (!width || width >= 300) {
+		img.setAttribute('data-action', 'zoom');
+	}
+});