Version constants for Lua

Pretty simple thing. Allows scripters to use VERSION, SUBVERSION, and VERSIONSTRING to check the game's version and potentially futureproof scripts. Have tested and confirmed working on my end.

Test script attached.
luatest-version.lua

Why not include CODEBASE and bump the vaule to 215, so scripts would know what is the codebase and be able to handle "API" breakage?

mentioned in commit e6f7b8ab

Status changed to merged