* default to LuaJIT when available
* add LuaBitOp for efficient bitwise operations in Lua
* make lib_bits use LuaBitOp if present
* add LuaBitOp licence notice
* fix CMake to work with LuaJIT/LuaBitOp, enforce C99
This improves the general building experience by integrating with the
newly created `sourceball` for windows. Most fixes involves either
adding `#ifdef WIN32` or replacing GCC-specific extensions with more
portable solutions.
Has been tested with MSVC 15 and MinGW64.
