Implement reading arrays into AnyLuaValue and AnyHashableLuaValue

[tpdickso]

This, as far as I can tell, solves the issue of recursive &mut crashing the compiler in the same way that it was solved in Push.

Tests are a bit hairy but I can't think of a cleaner way to write them at the moment.

[tpdickso]

This is a mildly breaking change, as it requires that AnyLuaValue and AnyHashableLuaValue be read from an AsMutLua as opposed to an AsLua, but this would always have been the case as long as the requirement on AsLua is not to touch the lua stack. Reading a table requires AsMutLua since as far as I know there's no way to do it without mutating the lua stack, so requiring only AsLua was probably incorrect to start with when LuaArray is a valid variant.

[tomaka]

I'm not sure exactly why &mut fixes it, but thanks! As for the breaking change aspect, it's not a problem.

[tpdickso]

My best guess is that it's a sort of a "linked list problem", where you can't have a struct Node { data: u32, next: Node }, but you can have a struct Node { data: u32, next: Box<Node> }, and casting lua to an &mut AsMutLua is the equivalent of adding that layer of indirection so that the compiler doesn't choke on itself trying to evaluate the recursive type. As to why that's necessary, I have absolutely no idea!