[implemented] api version variable in addon manifest

[sirinsidiator]

I was just wondering if it would be possible to add a new variable for the addon manifest so that we can make the addon compatible for both api versions on a major patch without having to clutter the code with

if(GetAPIVersion() == 100011) then 
--old 
else 
--new 
end

Something like

Startup_${apiversion}.lua

which then loads either Startup_100011.lua or Startup_100012.lua depending on the api version.