Adding options to set header and footer in PDF generation
Generate multiple page for ebook
Handle correctly exercises in ebook
Handle correctly quizzes
Improve style for exercises and quizzes in ebook
Remove old codes
Merge pull request #471 from GitbookIO/feature/multipages

Use multiple HTML files for ebook generation
Force type of header and footer templates
Merge branch 'alexandreaquiles-pdf_header_and_footer'
Remove ref to github options
Fix default for pdf templates
Adapt tests
Remove reference to single page output
Improve comments
Add link to gitbook.gitignore
Add unit test for quiz false positivies
Split section classification to separate files

Maybe have a sections folder in the future and one per type
(quiz/exercise/normal) ?
Ste GitBook as publisher
Fix #460: search for glossary term on all nodes
Rewrite quiz logic to be more robust

Fixes #470