[TW-229] history analysis

_Aikido Guy on 2011-08-27T19:27:32Z says:_

I have the following history:
```
$ task history

Year Month Added Completed Deleted Net
2011 February 49 8 7 34
March 67 46 6 15
April 45 35 6 4
May 31 30 3 -2
June 36 36 5 -5
July 25 25 2 -2
August 56 33 2 21

Average 44 30 4 9
```

I'd like, first, to have "Total" at the bottom. Should be easy to add, since that information is needed in order to calculate "Average".

Second, the history information is very useful but as a user I need to be able to take action based on what history reports to me. What actions could I perform after I see this history report? For example, if I'm trying to determine what caused a spike in August of the number of added tasks... namely, which projects contributed to this increase, what should I do? Would it be easy for history to have an option to break this report by all projects so that I could attempt to determine where the additional tasks originate? Or... maybe there is a more direct way that Taskwarrior could help me to determine this information? Perhaps, by reporting the set of projects that are for tasks within the "Net" task set.

More concretely,
1) I'd like to know which projects have tasks in the Net column.
2) I'd also be interested in getting a list of those specific tasks in the Net column.
3) This operation could be performed for a particular month/year... or perhaps, for any particular duration of interest.
4) This request may be more appropriate as a "history-details" or "history-analysis" command?

Thanks for a great tool... looking forward to using the next release!