feat(tour) content struct

this way, ID's can be managed separately from the content
feat(tour) initial content

@jbenet please review

If this is a desirable format, I will put in the rest so we can start to
make incrementatl progress on the actual copy.

Separated content from topic so Ids can be seen and modified without
excessive scrolling. Hopefully will make it easy to re-order content.
feat(tour) add file basics

keep things in one file for now
refactor(tour) extract chapters
docs(tour) comment Chapter func
docs(tour) Chapter
refactor(tour0 move chapter to it's own file
feat(tour) add node basics
feat(tour) merkledag chapter
feat(tour) network
feat(tour) routing
feat(tour) exchange, ipns
docs(tour) the rest
todo(tour) add
docs(tour) chapter
Merge pull request #269 from jbenet/tour-content-structure

feat(tour) content