Add SyntaxHighlighting

Big changes in this one. Sorry for the scary diff. :(

- Rename all markdown code blocks to have a matching language in a consistent format.
- Add `opn` task on `gulp watch` to launch the browser.
- `localhost:3000` serves from `dist/site`, which has a directory called `book-of-modern-frontend-tooling` to match our repo name (match how it's served from gh-pages). This was causing trouble loading our CSS file without adding a `base href="/book-of-modern-tooling/"`. Now, development and gh-pages will both work with the base href.
- Comment out the Google Analytics code until it's in use.
- Renamed `introduction.md` to `index.md` so an `index.html` is created.

Preview: http://stephenplusplus.github.io/book-of-modern-frontend-tooling/