Expand documentation

[natecraddock]

Now that I am finally consistently using Ziglua I am beginning to be annoyed at the terse documentation. It forces me to jump between the Lua docs and the Ziglua docs frequently. Now, Ziglua will never fully document the entire reference manual, but we can do better.

Update the docs to contain all needed information from the Lua docs. This includes the possible errors, push/pop from stack information, etc.

Completing this is a prerequisite for future changes. Adding or fixing code across the 4 Lua versions is tedious and while this will be a lot of work, it will pay off and make future work much easier.

[nurpax]

Suggestion: it'd be good to have example code on how to log the error messages coming from Lua, like when invoking code with pcall. Maybe even add some sort utility function that automatically turns on logging them (or utility for pcall that logs?)