Add optimistic locking support automatically for tables with a lock_version
Add documentation
Include lock_version support for update! and update operations
Fixed two comments that were transposed
Merge pull request #118 from loganb/optimistic_locking

Add optimistic locking support automatically for tables with a lock_version
Merge remote-tracking branch 'origin/master' into before_update_fix

Conflicts:
	lib/dynamoid/persistence.rb