Basic LuaJIT support + fixed compilation warnings

I'd also be glad to remove blobs (*.dll, *.exe) from repo, but unsure, if you accept pull request then.

I'd also glad to add normal luajit support (to let user select lua implementation via -DUSE*). But I can't do that with your current cmake files distribution without a dirty hacks or total rewriting (and I suggest to look how I realized that in lua-curl).