Recalculate ICESat-2 ATL11 height changes up to 20210715#329

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weiji14 wants to merge 5 commits intomainfrom

atlxi_dhdt_20210715

Commits on Oct 26, 2021

:chart_with_upwards_trend: Ice surface hrange and dhdt up to 20210715
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Commits on Oct 27, 2021

:sparkles: Calculate max slope of elev time-series using dhdt_maxslp
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Commits on Dec 13, 2021

Commits on Mar 27, 2022

:green_heart: Fix IndexError due to Lake Whillans 6 disappearing
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