added parameter to either null or error on missing years

[ssuffian]

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Description

Allows a parameter to be used that determines whether weather data with missing years of data returns an exception or NaNs.

[codecov[bot]]

Codecov Report

Merging #38 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #38   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          31     31           
  Lines        2577   2594   +17     
=====================================
+ Hits         2577   2594   +17

Impacted Files	Coverage Δ
eeweather/stations.py	100% <100%> (ø)	:arrow_up:
tests/test_stations.py	100% <100%> (ø)	:arrow_up:

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