Because "&" is not the last character to be unescaped, it is possible that
the lines for "<" and ">" expand some things they shouldn't.
For example, "&lt;" should become "<", but instead it becomes ">".
While this is unlikely to appear naturally in a notification, it is wrong.
This turns a hard-to-understand nested if{} chain into a simple switch
statement, and pulls some code out in to utility functions.
This is strictly a code-organization change, and should contain no
functional changes.
