Merge pull request #10 from lord63/master

Fix a typo in readme
Merge pull request #11 from lord63/master

Fix some typos
Add chapter about markdown
Add link to contact by email
Remove chapter about google authorship
Improve documentation about exercises and quizzes
Enable exercises and quizzes preview
gitbook.io -> Gitbook.io

- in the book it's always Gitbook.io except in the urls. Capitalize it
  to maintain consistency.
- fix lord63/documentation#1