Guide testing

The start of a testing guide. This PR relies on the crates and modules one because I shuffled some stuff around, so sorry about that.

I got stuck with how to import this name with cargo. @wycats and @alexcrichton , any ideas?
It seems that using bold markers for parts of words don't work in Markdown (at least on Github). `**item**s` will be rendered incorrectly (the second `**` are seen as part of the word) and should probably just be `**items**`.

Test:

- **items** works
- **item**s doesn't work