Getting userdata out of lua into C++ (after coming from C++ originally)

When you know a type is supposed to be a userdata with C++ information on it, there should be a way to get it out of the Lua VM and mess with it in C++ directly (since it is, indeed, a C++ object). This PR provides the ability to do that.

There are also several refactorings to reduce the amount of code written for get requests and friends.