Fix API links.

The book has been moved, so we should update the links.

Fixes #4555
Mime Type on HTML Emails

Some email readers can not interpret HTML emails without the MIME-Version set on the email header.
Mime Type on HTML Emails Fix

Some email readers can not interpret HTML emails without the MIME-Version set on the email header.
Fix for the MIME-TYPE be set by default
Merge pull request #4839 from lapenz/patch-3

Mime Type on HTML Emails
Fix failing tests.

Adding the MIME-Version header caused a few tests to fail.