Serialize the RenderBlogPost to JSON.

This struct still does not contain anything, but I'm just setting up the skeleton for this code.

src/blog_post/mod.rs

@@ -1,3 +1,5 @@
+mod convert;
 mod definition;
 mod render_context;
+pub(crate) use convert::convert_blog_post_to_render_context;
 pub(crate) use definition::BlogPost;