extract Ascii.compare

Before:

  $ time ./prog.out -lexer read ../data-for-lexing/test1600.json
  Reading input file
  Starting evaluation of Time = 1.282476 (for 160489 tokens)
  real	0m1.606s

After:

  $ time ./prog.out -lexer read ../data-for-lexing/test1600.json
  Reading input file
  Starting evaluation of Time = 0.272501 (for 160489 tokens)
  real	0m0.600s