Migrated sln and vcxproj files to Visual Studio 2019 to keep everything up to date. Changed directory name accordingly and added its build dirs to gitignore.
Fixed some compilation errors specific to the visual studio c++ compiler such as ambiguous casts, unused variables with duplicate names, typos and missed headers.
Modified the sdl, zlib and expat vcxproj projects to point to the new versions that have been updated in the 3rdparty directory. Add / remove new file references into the respective projects from within the new version directories as required for compilation and linking.
Flipped "treat warning as error" flags in some projects since there are some more warnings since moai 2.0 upgrade that were failing windows build otherwise.
Removed LuaJIT project references since it is currently unused in moai 2.0.
Added the necessary ZLIB_DEBUG flag in the new zlib project to get the debug builds to compile correctly. This is not added in the release builds.