Headers have ids and link to their own id.

CHANGELOG

app/assets/images/icon-link.png

app/assets/stylesheets/generic/files.scss

app/assets/stylesheets/generic/issue_box.scss

app/assets/stylesheets/generic/typography.scss

app/assets/stylesheets/main/mixins.scss

app/helpers/gitlab_markdown_helper.rb

app/views/help/_layout.html.haml

app/views/projects/issues/show.html.haml

app/views/projects/merge_requests/show/_mr_box.html.haml

app/views/projects/milestones/show.html.haml

app/views/projects/notes/_note.html.haml

doc/markdown/markdown.md

features/dashboard/help.feature

features/project/issues/issues.feature

features/project/issues/milestones.feature

features/project/merge_requests.feature

features/project/source/markdown_render.feature

features/steps/help.rb

features/steps/project/project_issues.rb