Ensure that outbound links are registered by GA

* Handle outbound links manually to ensure that they are registered
  with Google Analytics, as the previous method failed to do that.
* Remove the unused Google Analytics related code.
* Remove `js/main.js` and move its content into `index.html` (one
  less HTTP request).
* Use `htmlcompressor` to minify and obfuscate the inline script,
  as `htmlmin` doesn't have that feature.
Improve web performance

* Defer the downloading of the `YouTube player` and `tweet buttons`
  related code until after the page completely loaded.
* Remove the `logo.svg` reference (see: #105) from `index.html`, as
  it adds an extra HTTP request, without bringing much benefit.
* Remove the `logo.svg` (see: #105), as it only adds an extra HTTP
  request, without bringing much benefit.
* Specify image dimensions.