Tw2parser2

[img[ ]] still need to be sorted. 
I'd be inclined to remove them if we can.

Funnily enough, we have a similar problem with the current build process for classic.tiddlywiki.com. It pulls content in from tiddlywiki.tiddlyspace.com as a big JSON file. In order to get rid of the extraneous tiddlyweb fields I ended up rather ruining the `application/json` deserialiser by making it only accept the core known fields (see #238).

Soooooo, I guess what we really need here is a little batch .js to pull down just the core known fields from TiddlySpace, and then we can update the classic build process and finally fix #238.