Some feedback on documentation

[st0012]

These are the feedback from @yawniek on slack

• the vm.New vm.New and v.ExecInstructions methods would profit from some minimal documentation, especially what all the "paths" actually mean. some of them seemed semi obvious..
• same for RegisterExternalClass ExternalClass and vm.Method albeit those are relatively clear
• how can i load a class into toplevel so i dont need a require in the goby code?
• how can i load a method into the toplevel space / current vm context?
• in general a more clean example of whats done in db/plugin on how to interfer with go structs and their method would be super helpful, especially when it comes to handling and converting numbers,maps and slices.
• also explaining the details of the receiver vm.Object, sourceLine int, t *vm.Thread, args []vm.Object) vm.Object signature and how to efficiently work with it would be helpful