logarithmic plots with gr3_surface

use transformation functions for coordinates and colors.

Change-Id: I97b4ca18e5ded71cb9178a683c2fa774741ef269
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/14
Reviewed-by: Fabian Beule <f.beule@fz-juelich.de>
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
comments and GR3_SURFACE_NOGR option

Added comments.
Setting the 'surface' parameter of gr3_createsurfacemesh to
GR3_SURFACE_NOGR makes it detect the bounding box of the data by itself
instead from gr_inqwindow and gr_inqspace.

Change-Id: I5ef41d5094df5cd077a436f3b51594a71e791565
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/15
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Added gr3_surface examples

Change-Id: Id28d3747082a268b9512781daba58392d828f687
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/16
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>
Removed trailing blanks

Change-Id: I59ef7a51aa1f9843daa7db58fcca2d33672d864e
Reviewed-on: https://iffwww.iff.kfa-juelich.de/review/17
Reviewed-by: Josef Heinen <j.heinen@fz-juelich.de>