This PR includes various fixes to anchor links used in the documentation.
There are certain characters GitHub doesn't support for the use of anchor links in markdown files. The general rule I've found is to only use a-z or A-Z characters in anchor links. All other characters should be removed.
For example, consider the section title How do I connect to the Mailhog simulated server?. The valid GitHub anchor link for this section is #how-do-i-connect-to-the-mailhog-simulated-server. Notice no ?.
Closes#494