New JSON files

Includes breadcrumbs and links that point inwards not to HMRC site.
Rename manual_section_id to manual-section-id
Make anchors work

- Add anchors to sections
- Make links to sections have anchors
Refactor @document into presenter

Refactor document/section_group/section into presenters. Update views.
Put breadcrumbs onto page
Merge pull request #24 from alphagov/add-breadcrumbs

Add breadcrumbs