Add blog to docs (#484)

* Adding social card infrastructure
* Upgrades doc project to .NET 6
* Adds Playwright
* Changes the console to a web project for Playwright
* Adds social card template
* Added blog content
* Parallelized social image processing
* Updating CI to use .NET 6 for docs build

docs/input/blog/posts/2021-07-11-hello-world.md

@@ -0,0 +1,9 @@
+Title: Hello, World
+Description: To help track new releases, updates and planning for Spectre.Console, we've added a new blog to the documentation.
+Published: 20210711
+Category: News
+---
+
+To help track new releases, updates and planning for Spectre.Console, we've added a new blog to the documentation.
+
+Stay tuned for upcoming information related to the 0.41 release!

docs/input/blog/posts/BLOG_TEMPLATE.md

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+Title: Short title, less than 50 characters
+Description: Longer description, with optional *bold* and **italic** characters. Shouldn't be TOO long but can span multiple lines.
+Published: 20210710
+Category: Release Notes | News | or whatever
+Excluded: true
+---
+
+Intro paragraph, maybe even just the description. No need for a title that's included automatically.
+
+## Use second level headers
+
+Main title will be set with h1
+
+## Tasks
+
+1. Set title and description
+2. Set proper publish date
+3. Set proper category
+4. Remove excluded attribute.

docs/input/blog/posts/_ViewStart.cshtml

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+@{
+    Layout = @$"_layout.cshtml";
+}

docs/input/blog/posts/_layout.cshtml

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+@{
+    Layout = @"../../_layout.cshtml";
+}
+@inherits StatiqRazorPage<IDocument>
+
+@{
+    var author = Model.GetString("Author");
+    var published = Model.GetDateTime("Published");
+    var category = Model.GetString("Category");
+}
+
+@section subheading{
+<div class="mt-2 font-light text-xs md:text-sm">
+    <span>Posted </span>
+    @if (published != default(DateTime)) {
+        <span>@published.ToLongDateString() </span>
+    }
+    @if (author != null) {
+        <span>by @author </span>
+    }
+    @if (category != null) {
+        <span>
+            to <a class="text-blue-800 underline" href="@Context.GetLink($"blog/{NormalizedPath.OptimizeFileName(@category)}/index.html")">
+                @category
+            </a>
+        </span>
+    }
+
+</div>
+}
+
+
+
+@RenderBody()