Added stackdriver (https://www.stackdriver.com) plugin
Removed unnecessary variable
Used replace instead of split,join
Changed variable name which was creating confusion about data-point
Updated stackdriver.clj
Added riemann.time as requirement
Updated stackdriver.clj to accept vector of events
Updated stackdriver adapter
Updated stackdriver to omit events with nil as the metric value
Added docstring
Merge pull request #410 from pradeepchhetri/master

Added stackdriver plugin.