Adding calculations for stats

Tested using ```python2.6 bin/naarad -i examples/logs -o ~/tmp/neelix config-gc```

New files generated:

```
GC.stats.csv
```

and

```
GC.GC.percentiles.csv      GC.cmsCP.percentiles.csv   GC.commit.percentiles.csv  GC.gen0t.percentiles.csv   GC.used0.percentiles.csv
GC.alloc.percentiles.csv   GC.cmsCR.percentiles.csv   GC.commit0.percentiles.csv GC.gen0usr.percentiles.csv
GC.appstop.percentiles.csv GC.cmsCS.percentiles.csv   GC.commit1.percentiles.csv GC.promo.percentiles.csv
GC.apptime.percentiles.csv GC.cmsIM.percentiles.csv   GC.gen0.percentiles.csv    GC.safept.percentiles.csv
GC.cmsCM.percentiles.csv   GC.cmsRM.percentiles.csv   GC.gen0sys.percentiles.csv GC.used.percentiles.csv
```