Lua 5.4.2

This is a copy of the Lua source from https://www.lua.org with a CMake
build script added, which is tested working on 64-bit Windows 10.  It
produces the `lua` and `luac` executables, plus the static and shared
libs.

-- Building --

$ git clone https://github.com/phoenix-engine/lua lua-5.4.2
$ cd lua-5.4.2

$ mkdir build && cd build && cmake .. -DCMAKE_BUILD_TYPE=Release

$ cmake --build .

Obtain the target exe and/or libs from target/Release.  On Windows, the
symbol exports (lua_5_4_2.exp) are required (?) to use the DLL.

To use C libraries from Lua, or to use Lua as a C library, see
doc/manual.html#4 ("The Application Programming Interface").

-- Original README --

This is Lua 5.4.2, released on 13 Nov 2020.

For installation instructions, license details, and
further information about Lua, see doc/readme.html.