Add LuaJIT to benchmark

You think the parser performance of Lua is impressive? You haven't seen LuaJIT.

    ./benchmark.sh
    python               real 0m1.809s user 0m1.488s sys 0m0.316s
    ruby                 real 0m0.430s user 0m0.364s sys 0m0.060s
    lua                  real 0m0.161s user 0m0.152s sys 0m0.008s
    luajit               real 0m0.083s user 0m0.080s sys 0m0.000s
    python (precompiled) real 0m0.031s user 0m0.012s sys 0m0.016s
    lua (precompiled)    real 0m0.015s user 0m0.000s sys 0m0.012s
    luajit (precompiled) real 0m0.011s user 0m0.000s sys 0m0.008s
    
    Version Information:
    Python 2.7.3
    ruby 1.8.7 (2011-06-30 patchlevel 352) [x86_64-linux]
    Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
    LuaJIT 2.0.3 -- Copyright (C) 2005-2014 Mike Pall. http://luajit.org/