Python: Pass NODATA values to Python functions

[dbaston]

Resolves #136. Both values and weights will be masked arrays.

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.98%. Comparing base (bf8315a) to head (f4371dd).
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/raster_stats.h	96.15%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage   90.95%   90.98%   +0.03%     
==========================================
  Files          85       85              
  Lines        6332     6358      +26     
  Branches      622      627       +5     
==========================================
+ Hits         5759     5785      +26     
  Misses        541      541              
  Partials       32       32              

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[dbaston]

@JakubCha is this change OK on your end?

[JakubCha]

@JakubCha is this change OK on your end?

@dbaston checked with the current lib version after the merge and it seems to be fine in the plugin. As long as NODATA is correctly defined in the raster metadata, the plugin will return NULL if there are no valid pixels.