Port of python filters (predicate and programmable) to plugins; separate
test executables
use CMakeParseArguments in PDAL_ADD_TEST
accidently deleted wrong line in macro, fix it
fix broken SupportTest and python plugin options
use create<Reader|Writer|Filter> methods when creating driver stages,
especially for plugins, use unique_ptr's for stages
PCLVisualizer now has x, y, z, rgb, and intensity color handlers
Merge pull request #661 from PDAL/pcl-visualizer-improvements

PCLVisualizer now has x, y, z, rgb, and intensity color handlers
Merge pull request #659 from PDAL/move-python-filters

Move python filters
Merge pull request #662 from PDAL/stage-creation-tweak

use create<Reader|Writer|Filter> methods when creating driver stages,
Update PDAL_ADD_PLUGIN to use FILES and LINK_WITH keywords for passing
multiple arguments