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/book.toml

@@ -0,0 +1,22 @@
+[book]
+authors = ["Oleg Kalachev"]
+language = "ru"
+multilingual = false
+src = "book"
+title = "Полетный контроллер с нуля"
+description = "Учебник по разработке полетного контроллера квадрокоптера"
+
+[build]
+build-dir = "build"
+
+[output.html]
+additional-css = ["book.css", "zoom.css"]
+additional-js = ["zoom.js", "js.js"]
+edit-url-template = "https://github.com/okalachev/flix/blob/master/docs/{path}?plain=1"
+mathjax-support = true
+
+[output.html.code.hidelines]
+cpp = "//~"
+
+[preprocessor.alerts]
+command = "python3 alerts.py"