nsqd: make --statsd-interval take duration syntax and improve docs
nsqadmin: introduce --statsd-interval which is necessary for installations which dont use 60s
Merge pull request #218 from mreiferson/statsd_crap_218

nsqd/nsqadmin: improve statsd flush interval handling
nsqadmin: fix conversion of time.Duration to float64
Merge pull request #220 from mreiferson/float_fix_220

nsqadmin: fix large graphs