Define requirements for a language wrapper

[dethe]

We need a good document that explains what is possible and what is required for wrapping a language, including what methods need to be implemented or over-ridden. There is a good start at https://github.com/waterbearlang/waterbear/wiki/Setting-up-a-New-Language-in-Waterbear but it could be expanded on to talk about method over-rides and gotchas with non-JavaScript languages.