Documentation generated site, SEO and SOME-sharing

Search engine optimisations to improve F#-tooling-awareness.

Besides the current `` The templates should generate the following meta tags content to the page `<header>`, at least descriptions, keywords, etc:

```html
<meta property="og:site_name" content="Product name">
<meta name="description" content="Small description of the project." />
<meta name="keywords" content="fsharp" />
<meta property="og:image" content="http://non-ssl-path-logo.png">
<meta property="og:image:secure_url" content="https://.../logo.png">
<link rel="apple-touch-icon-precomposed" sizes="144x144" href="/logo.png" />
<meta name="twitter:card" content="summary_large_image" />
<meta name="twitter:site" content="@fsharporg" />
<meta name="robots" content="index,follow" />
<meta name="rating" content="general" />
```

I think url-routing is quite ok as it is, but the double-slash could be removed, e.g.:
https://moiraesoftware.github.io/myriad//tutorials/debugging.html