Implemented the 'DefaultIfEmpty' operator. See #34
Implemented 'cast' operator
Added the MSDN link
Added a klass parameter
Implemented the 'ofType' operator
Used 'cast' to remove SuppressWarnings
Used 'isInstance' to replace 'isAssignableFrom' and added a unit test
Merge branch 'master' into cast
Merge branch 'master' into default_if_empty
do not run RxScalaDemo on each build,

because it does not do automatic testing
Implemented 'Synchronize' with 'lock'
Merge pull request #409 from zsxwing/synchronize-lock

Implemented 'Synchronize' with 'lock'
Merge pull request #408 from samuelgruetter/idiomaticscala

Do not run RxScalaDemo on each build
Merge pull request #401 from zsxwing/default_if_empty

Implemented the 'DefaultIfEmpty' operator. See #34
Merge pull request #403 from zsxwing/cast

Implemented the 'cast' and 'ofType' operators
Merge branch 'master', remote-tracking branch 'origin'