Utilize new API features in examples

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We can simplify all of the Pandas related usage in the notebooks using some of the latest API features, for example:

url = 'https://api.cal-adapt.org/api/series/pr_day_HadGEM2-ES_rcp85/events/?g=POINT(-121.46+38.59)&imperial=y'
series = pd.read_json(url, typ='series', orient='split')

This instantiates a Series with date index and slug for the name attribute. This will help clean up some of the boilerplate in working with the API, such as unit conversions and requests code.