wb: call wb_putbuf() to mark hyphenation points
font: "ggrp" lines in font descriptions define character groups

Neatroff no longer supports the syntax |glyph for specifying
alternative glyphs.  That was very inefficient and produced large font
descriptions.  Instead, it is possible to define character groups:

  ggrp id n gl1 gl2 ... gln

In gpos and gsub lines, groups can be referenced using an @:

  ggrp 25 3 a c o
  gpos kern 2 T:+0+0-5+0 @25
font: inline glyph groups with only one glyph