fix: [breaking] enable saner settings default values for the book class

Breaking in the sense that it impacts how previous documents
appeared by default (esp. due to shaper.spaceenlargementfactor)
but the SILE defaults are utterly incorrect.

classes/resilient/book.lua

@@ -114,11 +114,17 @@ function class:_init (options)
   self:loadPackage("resilient.headers")
   self:loadPackage("markdown")
 
-  -- override document.parindent default
+  -- Override document.parindent default:
   SILE.settings:set("document.parindent", "1.25em")
+  -- Override with saner defaults:
+  -- prefer underfull lines over ugly overfull content
+  SILE.settings:set("linebreak.emergencyStretch", "25%lw")
+  -- This should never have been 1.2 by default
+  SILE.settings:set("shaper.spaceenlargementfactor", 1)
 
-  -- override the standard foliostyle hook to rely on styles
+  -- Override the standard foliostyle hook to rely on styles
   -- TRICKY, TO REMEMBER: Such overrides cannot be done in registerCommands()
+  -- as packages are not loaded yet.
   self:registerCommand("foliostyle", function (_, content)
     SILE.call("noindent")
     local styleName = SILE.documentState.documentClass:oddPage() and "folio-odd" or "folio-even"