Merge pull request #19 from Dshankar/master

added getRooms
[feature] Adding primus.rooms method
[doc] Adding primus.rooms documentation
[fix] Small fix
[fix] Small correction
[minor] clients method refactoring
[minor] primus.isRoomEmpty change
[test] Some minor changes
[test] Some minor changes
[release] 2.2.0
minor fix on README for leaveallrooms event