Fixed typos
Merge pull request #52 from pborreli/typos

Fixed typos
Fix typo
Added CONTRIBUTING.md file
Merge pull request #55 from Bladrak/contributing

Added CONTRIBUTING.md file
Fixing typo
Merge pull request #56 from grosenbaum/fix-typo

Fixing typo
Merge remote-tracking branch 'refs/remotes/sonata-project/master'