remove _get_sys_info
Added a "combine" function to add two nfsiostats together
Added NFS Aggregation

* Changed the update function to use an nfs_stats_old instead of
nfs_mountstats. That allows me to store other arbirary values, such
as "ALL"

* Utilized the newly added "combine" function to add all the stats
together as we are looping through the devices

* Added a couple new config items to determine whether we want to
report all volumes, and/or aggregate data.
Bump Version to 0.2.2
Merge pull request #5 from TJM/aggregate-stats

Aggregate NFS stats