Begin using 'option' rather than 'set' for PDAL options
Begin using 'option' rather than 'set' for PDAL options

Options become slightly more concise (drops the 'CACHE BOOL') and
enables use of CMAKE_DEPENDENT_OPTION macro, which could be useful
for the GDAL/GeoTIFF/TIFF trio among others.

mpgerlek/PDAL-old,jwomeara/PDAL,radiantbluetechnologies/PDAL,Sciumo/PDAL,mpgerlek/PDAL-old,boundlessgeo/PDAL,Sciumo/PDAL,jwomeara/PDAL,DougFirErickson/PDAL,mtCarto/PDAL,jwomeara/PDAL,radiantbluetechnologies/PDAL,Sciumo/PDAL,boundlessgeo/PDAL,mpgerlek/PDAL-old,mtCarto/PDAL,lucadelu/PDAL,boundlessgeo/PDAL,DougFirErickson/PDAL,DougFirErickson/PDAL,mtCarto/PDAL,jwomeara/PDAL,lucadelu/PDAL,mpgerlek/PDAL-old,Sciumo/PDAL,boundlessgeo/PDAL,lucadelu/PDAL,lucadelu/PDAL,radiantbluetechnologies/PDAL,mtCarto/PDAL,radiantbluetechnologies/PDAL,DougFirErickson/PDAL