Merge pull request #52 from adennie/add-dot-checkstyle-to-gitignore

add .checkstyle file (generated by Eclipse checkstyle plugin) to .gitignore
Merge pull request #49 from adennie/remove-checkstyle-doublechecked-locking

remove module DoubleCheckedLocking (no longer supported as of Checkstyle...
fix compiler warning about use of unparameterized Comparable declaration.
Replaced Comparable with Serializable.
Merge branch 'fix-comparable-warning'