Method fix

chapter24/src/main/java/com/seaofnodes/simple/util/SB.java:48–52

( int sz, String s )

  // Fixed width field
  public SB fix( int sz, String s ) {
    for( int i=0; i<sz; i++ )
      _sb.append( i < s.length() ? s.charAt(i) : ' ');
    return this;
  }
  public char at(int idx ) { return _sb.charAt(idx); }

  // Not spelled "p" on purpose: too easy to accidentally say "p(1.0)" and