Merge pull request #5 from jaspernbrouwer/master

Refactored BookId
Merge pull request #6 from jaspernbrouwer/master

Renamed namespace back & added PersonId and ISBN
added BookWasAdded event
added BookWasDiscarded event
added BookWasCheckedOut event
added BookWasReturned event
Merge pull request #7 from jaspernbrouwer/master

Added commands
added BookWasAdded event
fixed merge commit due to bad branching
Merge pull request #8 from ramondelafuente/master

added events