Added support to delete a specific version of a file.
Removed TODO comment.
Fixed the param names for javadoc
Merge branch 'master' of github.com:raj-saxena/box-java-sdk-v2
Changes for 1)Adding collaboration for a group 2)Promoting an old version of files as current.
Merge branch 'master' of github.com:box/box-java-sdk-v2
Merge pull request #220 from raj-saxena/master

Changes for 1) Deletion of a particular version of file. 2) Adding collaboration for a group. 3) Promoting an old version of files as current.