Fixed non-functional bold tags

Since Markdown won't parse bold tags in the middle of text, I changed it to code tags, which are parsed.
This makes the variables stand out more than two stars, as well as making it look better.

### TL;DR

http(s)://api.4chan.org/**board**/**pagenumber**.json **becomes ->**
http(s)://api.4chan.org/`board`/`pagenumber`.json