LuaJIT support

[thalting]

TODO: turn this into a build flag.

[endaaman]

Thanks for the PR.

I think this should be the compile option to enbale by like --enable-luajit.

[thalting]

how can I do this?

[endaaman]

What you have to do

• Edit configure.ac, introduce --with-luajit option and define the flag that luajit is enabled or not.
• Write LuaJIT-supported code along with the flag.
• Fix Dockerfile or add new test suite for LuaJIT compilation.

[thalting]

i don't know how to use autotools :/

[thalting]

--enable-luajit by @capezotte

[endaaman]

--enable-luajit and USES_LUAJIT are defined but it seems LuaJIT is not actually used.

[thalting]

[ecesar88]

merge?

[endaaman]

I wanted the review fixed. Anyway, it is OK. I will fix it.
Thanks for the PR!