Fix a few deprecation warnings

[DanielGoldfarb]

1. MatplotlibDeprecationWarning: The seaborn styles shipped by Matplotlib are deprecated since 3.6, as they no longer correspond to the styles shipped by seaborn. However, they will remain available as 'seaborn-v0_8-<style>'. Alternatively, directly use the seaborn API instead.

   • try style 'seaborn-v0_8-darkgrid', if exception then use old 'seaborn-darkgrid'

2. FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.

   • use concat() instead of append()

3. FutureWarning: iteritems is deprecated and will be removed in a future version. Use .items instead. for date,value in percentB.iteritems():

   • use items() instead of iteritems()

4. <string> DeprecationWarning: invalid escape sequence \

   • use raw string for docstring that contains an un-escaped \