Main book: Fix \setbookmaintitle

The main title of the Tutorials book wasn't updated to the new bookpart syntax
jbSongbooks: Initial version

This tutorial was submitted by email,
so this commit is a complete first version
jbSongbooks: clean up formatting

clean up the formatting of the initial email contribution.
Main changes:
- Remove spaces inside \texttt{} commands
- Change \texttt to \cmd or \package
- split lines to one sentence per line