Added additional tests to the geotiff reader and also added so that if the GDAL unofficial NODATA tag is present, that NODATA value in the image bytes is replaced by GeoTrellis NODATA value.
Added test to check reading of ESRI produced geotiff.
Merge pull request #2 from lossyrob/feature/geotiff-reader-unit-test-adds

Added test to check reading of ESRI produced geotiff.
Added failing test for reading slope.tif
Merge pull request #3 from lossyrob/feature/geotiff-reader-unit-test-adds

Added failing test for reading slope.tif
ESRI file test passes with NODATA value and another unit test for converting byte tiled images to byte row images added and passing.
Merge branch 'feature/geotiff-reader-unit-test-adds' of github.com:johanstenberg92/geotrellis into feature/geotiff-reader-unit-test-adds
slope.json unit test works.
Now parsing ESRI/GDAL NODATA tag as a direct double. Also removed a unit test for image conversion from tiles to rows which had an invalid number of bits per pixel. This case is covered in the GeoTiffReaderSpec instead so no functionality is less tested than before.
Merged in upstream
Modified how NoData is replaced, for speed's sake.
Merge pull request #842 from lossyrob/feature/geotiff-reader-unit-test-adds

Added additional tests to the GeoTiff reader and NoDATA replacement