performance_analytics.category_nav
**********************************

spice.performance_analytics.category_nav(nav_data: DataFrame) -> Series

   Generates the category(or peer group) NAV by first normalizing the
   NAV series of multiple funds to a common starting point, and then
   averaging the normalized series. Directly averaging raw NAV values
   would be misleading since funds can have very different absolute
   NAV levels.

   Parameters:
      **nav_data** -- A DataFrame with date as index and columns
      containing NAV values for different funds/series. It should not
      have the benchmark timeseries.

   Returns:
      Series with category NAV values indexed by date

   Return type:
      pd.Series

   -[ Example ]-

   >>> nav_df = pd.DataFrame({
   ...     "Fund A": [100, 101, 102],
   ...     "Fund B": [200, 201, 202],
   ...     "Fund C": [150, 151, 152]
   ... }, index=pd.to_datetime(["2023-01-01", "2023-01-02",
   ...                          "2023-01-03"]))
   >>> result = category_nav(nav_df)
