detect hitting max upvalue limit

[bubaflub]

At work we had some code that triggered the compilation error, "function at line ___ has more than 60 upvalues". While our testing caught it, I think luacheck could also find and flag these issues as well.

60 is the default defined somewhere and I suppose someone could override it and recompile. If we check for this, we should also have a configuration option that specifies this limit.

[mpeterv]

Limit is 255 for Lua 5.2 and Lua 5.3. For now I'll set default limit to limit of Lua version used to run luacheck.