paper size and global font size: simplify input

[Graham Percival]

A few months ago, we discussed being able to set these items in the 
normal lilypond way, ie

\paper {
  #(set-paper-size "a4")
  paper-size = "a4"      % proposed new method
}

#(set-global-staff-size 14)
\paper {
  global-staff-size = #14     % proposed new method
}

I'm working on the new chapter on spacing and page stuff, and I was 
reminded of our current ugly method of setting these.  Could somebody 
make this change?
- Graham