ENH: allow saving of meta-data via CArrays to support wide tables
supersedes #10243 
closes #6245

Here is the code as it stands now.  Appending MultiIndex axes now works.  The one test that still fails is  test_append_frame_column_oriented: writing the DateTimeIndex as columns fails because the index is converted to an array of timestamps so np.array creates an object array.  If it could be passed down unmolested np.array() would do the right thing.  I don't yet have a good idea how to fix that.

I added a test for reading the old format, let me know if you think it's sufficient coverage.  I've been testing the reading more broadly against my own data.  
