ENH: vbench support for HDFStore
added benchmarcks to compare (100,000) rows:
- read/write store
- read/write store mixed
- read/write table
- read/write table wide (200 columns)
- read/write table mixed
- query wide/table

The start dates on these are too early (they use newer apis)
 true....so a lot will fail, but read/write store should work
what date is a good start point?
 i started with io_bench.py....that's where they came from
 Maybe like 2012-07-01 or so. Anytime 0.8.0 onward should be OK. If you go to some effort you can make the tests work on earlier pandas but prolly not worth the effort
 just check 7.0...should work for that (not the mixed types or queries...but evrything else)...2/1/12?
 done
 thanks!
