refactor: track tlua error locatio

When lua raises an error from the code loaded with tlua::exec() and tlua::eval(), it looks as follows:

[string \"chunk\"]:1: oops

It gives no useful information and complicates debugging.

With this patch, lua errors will correctly point to the place where exec() was called, e.g.:

[tests/src/tlua/lua_functions.rs:216]:6: oops