DEM: Shaded relief image plot (digital elevation model)

- improves the colormap splitting between land and sea
- new option 'lakezmin' to limit lake detection

- new option 'position' for tick labels
- major update thanks to mas Wiwit

minor fix

legend scale is now liberated from the figure colormap (thanks to Tomke Froechtenich's comment). No use of freezecolors needed to add other colormap plots.

improve backward compatibility (strjoijn)

- new options: 'km', 'watermark', 'fontsize', 'bordersize'
- improve legend colorbar
- all options now passed as param/value

- improved light rendering (using surface normals instead of gradient)
- improved 'lake' detection algorithm
- new 'nancolor' option to set NaN color
- adds a length scale with 'dec' option
- minor code improvements

- adds 'interp' option (fill the gaps)
- adds 'seacolor' colormap for negative elevations (bathymetry)

- adds a 'lake' option
- minor bug correction

now accepts row/column vectors for X and/or Y.

- adds basemap-style axis in decimal or lat/lon modes
- adds elevation and distance scales

- new landcolor.m colormap function
- new arguments to control colormap scaling
- median-style filters for light and colormap

ZIP now contains landcolor.dat companion file.

Optimizations: adds a decimation for large DEM grids.