fix passing self to metamethods, and add t=self arg syntax

[Numynum]

devtool will already automatically pass the parent to a function, if the function returns an error (though that's not helpful for functions that simply return nil, when no valid parent is passed)
but this was broken when using __index metamethods that are tables, and only worked for __index metamethods that are functions

in addition, I always felt like it'd be nice to be able to explicitly pass the self argument, so I also added t=self as an argument

comparing to DevTool.list, is needed to fix an error with GetParentTable returning DevTool.list, for functions that are added directly, e.g. through DevTool:AddData(someFunc)

[Numynum]

since I made an example screenshot already anyway, might as well add it here 🙂

[brittyazel]

Great addition! Thanks for adding this. I look forward to using it :-)