Generate hue-saturation-lightness colormaps

USAGE: hslcolormap(N,H,S,L)

INPUTS:
N: number of colors in colormap.
H: hue stops (optional). %can also be specified using a string: rygcbmRYGCBM
S: saturation stops (optional)
L: Lightness stops (optional)

The stops are placed evenly over the colorscale. Parameter examples:
H=[0 1/6]; %colorscale runs from red to yellow
S=[0 1]; %gray to fully saturated
L=[.3 1 .3]; % dark-bright-dark

Using L with two-stops (e.g. L=[.2 .8]) makes it easy to distinguish
high and low values.

Using a symmetric L with 3 stops (e.g. L=[.2 1 .2]) is useful for divergent
colorscales.

Discontinuities in the colormap can be indicated with nans.


EXAMPLE:
surf(peaks(200),'edgecolor','none');
caxis([-6 6])
hslcolormap(300,'g.m',1,[.1 1 .1]);
colorbar




(c) Aslak Grinsted 2014