feat(content): routing to provided .blog paths

This is a starting point to dynamically loading `markdown` files as blog
entries. With this change the *doc/about.md* and *doc/blog.md* files
are no longer builded into the executable and instead read from the
filesystem during runtime (along with the new test file *doc/test.md*).

doc/test.md

@@ -0,0 +1,51 @@
+---
+title: Capabilities of tui-website
+---
+Not everything that can be done with markdown can be representented by this tui-application. It is simple enough to
+support basic markdown files. Currently the text has to be manually reflowed to 120 characters, such that there is no
+issue when rendering (i.e. correct line breaks, etc.)
+
+The following list contains all the available features that are supported (with some examples below):
+
+  - unordered lists (using `-`, `+` and `*`, where the corresponding symbol is used when rendering)
+  * links
+  + blocks
+  - `inline blocks` (written as `inline blocks`)
+  * _italic_ (written as `_italic_`)
+  + **bold** (written as `**bold**`)
+  - headlines (corresponding sub heading six levels deep)
+
+Headings currently require a second newline before the list items to render correctly with a empty line in between the
+following contents and the last list item.
+
+Another paragraph.
+
+# Examples
+
+> quotes are not supported (yet)
+
+The following is a block. Which renders as follows (containing line numbers and **no code highlighting**):
+
+---
+
+```zig
+fn myFunction() void {
+    if (hasFeature()) {
+        // Feature-specific code
+    } else {
+        // Default code
+    }
+}
+
+inline fn hasFeature() bool {
+    return (comptime comptimeCheck()) and runtimeCheck();
+}
+```
+
+## Combinations are possible
+
+1. see this excellent blog post: [Conditionally Disabling Code with comptime in Zig - Mitchell Hashimoto](https://mitchellh.com/writing/zig-comptime-conditional-disable)
+
+### See deeper levels are possible and will be rendered correctly
+
+This is just some placeholder text.