ADD: updraft structure analysis and iterative test

Adding two notebooks, one which is my preliminary investigation with
characterizing updraft structures (e.g., shape and intensity), and the
other which is my testing of the iterative wind retrieval method.
Adding analysis notebooks!

Adding two analysis notebooks involving the reflectivity comparison
between the CSAPR and UAZRKAZR on 25 April 2011 and the wind retrieval
comparison between the 3D-VAR method and the UAZR.
Lots of pickle notebooks!

This commit contains some new pickling notebooks and some changes to
older pickling notebooks. The changes are relatively minor, but some are
significant, e.g., modified to handle new winds output from
_check_analysis. The new notebooks added should be self explanatory!