On Nook and A5 prints, start a new page with each tune and centre vertically..

A5 mostly did, but ran into trouble with longer comments on a tune.
This may give blank space after tunes where a long comment overflows
onto another page, but I think for now it's better to have each tune
at the top of the page.

Or rather, and this is the other change, in the middle of the page. Centre
the page content for A5 and Nook.

docsetup.A4.tex

@@ -38,3 +38,5 @@
 
 % Page appearance.
 \newcommand*{\pagestylemod}{}
+\newcommand*{\tunestart}{}
+\newcommand*{\tuneend}{\vfill}

docsetup.A5.tex

@@ -36,3 +36,5 @@
 
 % Page appearance.
 \newcommand*{\pagestylemod}{}
+\newcommand*{\tunestart}{\newpage \topskip0pt \vspace*{\fill}}
+\newcommand*{\tuneend}{\vspace*{\fill}}

docsetup.Nook.tex

@@ -24,3 +24,5 @@
 \newcommand*{\pagestylemod}{\begingroup
 \cfoot{}
 \endgroup}
+\newcommand*{\tunestart}{\newpage \topskip0pt \vspace*{\fill}}
+\newcommand*{\tuneend}{\vspace*{\fill}}

dottes.tex.tune

@@ -1,5 +1,6 @@
+\tunestart
 \showtune{$name}{$title}{$subtitle}{$fulltitle}{$tradition}{$composer}{$parts}{$graphicsdir/$name}
 $notes
 
 $history
-\vfill
+\tuneend