Update IvoryTower.java
double-checked-locking pattern is added.
Update pom.xml

test dependency is added.
Update IvoryTower.java

fixed the issue with class creation.
Added Double Checked Locking to documentation.
Added class diagram to double checked locking.
Added cases to use double-checked-locking.
Added simple attributes to the Item.
Merge branch 'master' of github.com:yusufaytas/java-design-patterns
removed the lazy instantiation from singleton to avoid threading
problems.
Added Intent to the Double Checked Locking.
Merge pull request #1 from yusufaytas/master

Update creating mechanism.