Fix dimensions for several output variables

Fix dimensions for several output variables

* Dimensions for the following output variables are now
  interpreted correctly since they have been added to the
  dimension-variables variable (heeding the warning at the
  top of ly/paper-defaults.ly):

  after-title-space
  before-title-space
  between-title-space
  bottom-margin
  foot-separation
  head-separation
  top-margin

* page-turn-page-breaking-badturns.ly: slightly adjusted

* NR 4.6: general rewrite, with updated information

Signed-off-by: Patrick McCarty <pnorcks@gmail.com>