reduce spacing between lyrics lines

This commit entails major changes in the songbook appearance since songs need less vertical space. Advantages:
  - saves roughly 100 pages for songbook.pdf !
  - less scrolling / page turning required
  - better readability due to more important delta between inter-verse spacing and inter-line spacing

tex/crepbook.cls

@@ -359,10 +359,10 @@
 % Horizontal space reserved to verse number
 \setlength{\versenumwidth}{1em}
 % Modifier to the space between consecutive lines of lyrics
-\baselineadj=-2pt plus 1pt minus 1pt
+\baselineadj=-6pt plus 4pt minus 4pt
 % Space between verses and chorus
 \versesep=6pt plus 2pt minus 2pt
-%lyrics font
+% lyrics font
 \renewcommand{\lyricfont}{\normalfont\normalsize}