MSON AST reflecting the new specification

For @fosrias, @honzajavorek and @pksunkara to review. 
> The code working with the MSON AST would have to check for descriptions in two different kind of places.

That is correct. However this is a main flaw of the Snow Crash parsing API Blueprint – as it does some optimizations it should and then you are never able to produce the original source from the AST. In other words in API Blueprint AST – the AST isn't really 1:1 with what is written in blueprint.