Added perceptually uniform fire colormap #943
The "hot" colormap that is the default for Image and other Raster types in Holoviews is highly perceptually nonuniform, which makes strange artifacts and makes it difficult to interpret data:
On my request, Peter Kovesi created a much better version he called linear_kryw_0_100_c71 (see http://peterkovesi.com/projects/colourmaps):
The new colormap (left) gives much smoother images that more faithfully represent the data:
This PR adds the new colormap, renamed "fire" for simplicity and to indicate the similarity to "hot". A subsequent PR should change the default colormap to "fire".