Merge branch 'release/0.0.2'
Fixed bad var name introduced in 0.0.2
Band finding should return nil if the band isn't found
Handle when no default histogram
Made calculate_ndvi a class method
Default approx_ok to false
Fixed #histogram not returning totals
Refactored histogram methods
Run tests for all raster bands
Bump to 0.0.3
Merge branch 'hotfix/bugs' into develop