Minor proofreading corrections to Hugo docs

- Add backticks and commas where necessary
- Remove some trailing whitespace
- Add front matter example in TOML
- Fix typo in one of the tags in Showcase
- Add 多说 (Duoshuo) as an alternative to Disqus
- Use internal links (i.e. without gohugo.io) where possible
- Use a colon to set off an example
- Change "it's" to "its" where appropriate
- Use typographical (i.e. curly) apostrophe on the front page
  where appropriate
- Capitalize "Github" as "GitHub"

docs/content/tutorials/github_pages_blog.md

@@ -175,7 +175,7 @@ To build all draft posts *(If you only have drafts, no site will be generated)*
 
     #!/bin/bash
 
-    echo -e "\033[0;32mDeploying updates to Github...\033[0m"
+    echo -e "\033[0;32mDeploying updates to GitHub...\033[0m"
 
     # Build the project. 
     hugo